Squashed 'apollo-ios/' changes from d09a8c6..3901362

3901362 Make ApolloInterceptor id requirement read-only (#159)

git-subtree-dir: apollo-ios
git-subtree-split: 3901362

Sources/Apollo/ApolloInterceptor.swift

@@ -10,7 +10,7 @@ public protocol ApolloInterceptor {
   /// Each operation request has it's own interceptor request chain so the interceptors do not
   /// need to be uniquely identifiable between each and every request, only unique between the
   /// list of interceptors in a single request.
-  var id: String { get set }
+  var id: String { get }
 
   /// Called when this interceptor should do its work.
   ///