Use node groups in node patterns to replace unions of types

`rubocop-ast` defines some node groups (https://github.com/rubocop/rubocop-ast/blob/master/lib/rubocop/ast/node.rb#L89-L116) that can be used inside node pattern matchers in place of a union of node types.

lib/rubocop/cop/capybara/rspec/predicate_matcher.rb

@@ -44,7 +44,7 @@ def check_inflected(node)
 
           # @!method be_bool?(node)
           def_node_matcher :be_bool?, <<~PATTERN
-            (send nil? {:be :eq :eql :equal} {true false})
+            (send nil? {:be :eq :eql :equal} boolean)
           PATTERN
 
           # @!method be_boolthy?(node)