Make GraphQLType conform to Hashable

Author: lukel97

Sources/GraphQL/Type/Definition.swift

@@ -4,7 +4,7 @@ import NIO
 /**
  * These are all of the possible kinds of types.
  */
-public protocol GraphQLType      : CustomDebugStringConvertible, Encodable, KeySubscriptable, AnyObject, Equatable {}
+public protocol GraphQLType      : CustomDebugStringConvertible, Encodable, KeySubscriptable, AnyObject, Hashable {}
 extension GraphQLScalarType      : GraphQLType                             {}
 extension GraphQLObjectType      : GraphQLType                             {}
 extension GraphQLInterfaceType   : GraphQLType                             {}
@@ -16,7 +16,11 @@ extension GraphQLNonNull         : GraphQLType                             {}
 
 extension GraphQLType {
     public static func == (lhs: Self, rhs: Self) -> Bool {
-        ObjectIdentifier(lhs) == ObjectIdentifier(rhs)
+        lhs === rhs
+    }
+    
+    public func hash(into hasher: inout Hasher) {
+        ObjectIdentifier(self).hash(into: &hasher)
     }
 }