Implement __ne__ method consistently

Author: Cito

src/graphql/error/graphql_error.py

@@ -169,7 +169,7 @@ def __eq__(self, other):
         )
 
     def __ne__(self, other):
-        return not self.__eq__(other)
+        return not self == other
 
     @property
     def formatted(self):

src/graphql/error/invalid.py

@@ -20,7 +20,7 @@ def __eq__(self, other):
         return other is INVALID
 
     def __ne__(self, other):
-        return not self.__eq__(other)
+        return not self == other
 
 
 # Used to indicate invalid values (like "undefined" in GraphQL.js):

src/graphql/language/ast.py

@@ -169,7 +169,7 @@ def __eq__(self, other):
         return False
 
     def __ne__(self, other):
-        return not self.__eq__(other)
+        return not self == other
 
     def __hash__(self):
         return hash((self.start, self.end))