Fix dialyzer errors, and make dialyzer part of the CI build

[freshtonic]

leexinc.hrl:268: Function yyrev/2 will never be called
executor.ex:31: The specification for 'Elixir.GraphQL.Execution.Executor':execute/3 states that the function might also return {'ok','Elixir.Map'} but the inferred return is {'error',<<_:296,_:_*128>> | #{}} | {'ok',_,_}
executor.ex:43: The specification for 'Elixir.GraphQL.Execution.Executor':execute_operation/3 states that the function might also return {'ok','Elixir.Map'} but the inferred return is {'error',<<_:296,_:_*128>>} | {'ok',_,_}
executor.ex:88: Overloaded contract for 'Elixir.GraphQL.Execution.Executor':execute_fields/4 has overlapping domains; such contracts are currently unsupported and are simply ignored
executor.ex:137: The call 'Elixir.GraphQL.Execution.Executor':complete_value_catching_error(context@1::atom() | tuple() | #{},return_type@1::any(),field_asts@1::nonempty_maybe_improper_list(),info@1::#{},result@1::any()) breaks the contract ('Elixir.GraphQL.Execution.ExecutionContext':t(),any(),'Elixir.GraphQL.Document':t(),any(),#{}) -> {'Elixir.GraphQL.Execution.ExecutionContext':t(),#{} | 'nil'}
executor.ex:146: Invalid type specification for function 'Elixir.GraphQL.Execution.Executor':complete_value_catching_error/5. The success typing is (_,_,nonempty_maybe_improper_list(),#{},_) -> any()
executor.ex:152: Overloaded contract for 'Elixir.GraphQL.Execution.Executor':complete_value/5 has overlapping domains; such contracts are currently unsupported and are simply ignored
executor.ex:191: The created fun has no local return
executor.ex:192: The call 'Elixir.GraphQL.Execution.Executor':complete_value_catching_error(context@2::any(),list_type@1::any(),field_asts@1::nonempty_maybe_improper_list(),info@1::#{},item@1::any()) breaks the contract ('Elixir.GraphQL.Execution.ExecutionContext':t(),any(),'Elixir.GraphQL.Document':t(),any(),#{}) -> {'Elixir.GraphQL.Execution.ExecutionContext':t(),#{} | 'nil'}
resolvable.ex:2: The specification for 'Elixir.GraphQL.Execution.Resolvable':'__protocol__'/1 states that the function might also return 'true' but the inferred return is 'Elixir.GraphQL.Execution.Resolvable' | 'false' | [{'resolve',4},...]
type_info_visitor.ex:124: Call to missing or unexported function 'Elixir.GraphQL.Lang.AST.TypeInfo':nullable_type/2
visitor.ex:3: The specification for 'Elixir.GraphQL.Lang.AST.Visitor':'__protocol__'/1 states that the function might also return 'true' but the inferred return is 'Elixir.GraphQL.Lang.AST.Visitor' | 'false' | [{'enter',3} | {'leave',3},...]
visitor.ex:48: The specification for 'Elixir.GraphQL.Lang.AST.InitialisingVisitor':'__protocol__'/1 states that the function might also return 'true' but the inferred return is 'Elixir.GraphQL.Lang.AST.InitialisingVisitor' | 'false' | [{'init',2},...]
visitor.ex:64: The specification for 'Elixir.GraphQL.Lang.AST.PostprocessingVisitor':'__protocol__'/1 states that the function might also return 'true' but the inferred return is 'Elixir.GraphQL.Lang.AST.PostprocessingVisitor' | 'false' | [{'finish',2},...]
abstract_type.ex:1: The specification for 'Elixir.GraphQL.Type.AbstractType':'__protocol__'/1 states that the function might also return 'true' but the inferred return is 'Elixir.GraphQL.Type.AbstractType' | 'false' | [{'get_object_type',3} | {'possible_type?',2} | {'possible_types',2},...]
definition.ex:3: The specification for 'Elixir.GraphQL.Types':'__protocol__'/1 states that the function might also return 'true' but the inferred return is 'Elixir.GraphQL.Types' | 'false' | [{'parse_literal',2} | {'parse_value',2} | {'serialize',2},...]
Unknown functions:
  'Elixir.GraphQL.Execution.Resolvable.BitString':'__impl__'/1
  'Elixir.GraphQL.Execution.Resolvable.Float':'__impl__'/1
  'Elixir.GraphQL.Execution.Resolvable.Integer':'__impl__'/1
  'Elixir.GraphQL.Execution.Resolvable.List':'__impl__'/1
  'Elixir.GraphQL.Execution.Resolvable.Map':'__impl__'/1
  'Elixir.GraphQL.Execution.Resolvable.PID':'__impl__'/1
  'Elixir.GraphQL.Execution.Resolvable.Port':'__impl__'/1
  'Elixir.GraphQL.Execution.Resolvable.Reference':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.Atom':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.BitString':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.Float':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.Function':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.Integer':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.List':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.Map':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.PID':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.Port':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.Reference':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.InitialisingVisitor.Tuple':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.Atom':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.BitString':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.Float':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.Function':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.Integer':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.List':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.Map':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.PID':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.Port':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.Reference':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.PostprocessingVisitor.Tuple':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.Atom':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.BitString':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.Float':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.Function':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.Integer':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.List':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.Map':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.PID':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.Port':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.Reference':'__impl__'/1
  'Elixir.GraphQL.Lang.AST.Visitor.Tuple':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.Atom':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.BitString':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.Float':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.Function':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.Integer':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.List':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.Map':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.PID':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.Port':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.Reference':'__impl__'/1
  'Elixir.GraphQL.Type.AbstractType.Tuple':'__impl__'/1
  'Elixir.GraphQL.Types.Atom':'__impl__'/1
  'Elixir.GraphQL.Types.BitString':'__impl__'/1
  'Elixir.GraphQL.Types.Float':'__impl__'/1
  'Elixir.GraphQL.Types.Function':'__impl__'/1
  'Elixir.GraphQL.Types.Integer':'__impl__'/1
  'Elixir.GraphQL.Types.List':'__impl__'/1
  'Elixir.GraphQL.Types.Map':'__impl__'/1
  'Elixir.GraphQL.Types.PID':'__impl__'/1
  'Elixir.GraphQL.Types.Port':'__impl__'/1
  'Elixir.GraphQL.Types.Reference':'__impl__'/1
  'Elixir.GraphQL.Types.Tuple':'__impl__'/1
Unknown types:
  'Elixir.GraphQL.AbstractType':t/0
 done in 0m8.20s
done (warnings were emitted)

[freshtonic]

We've not been keeping on top of this. We should :)