Fixed Argument comparison. Fixed #530

Author: syrusakbary

graphene/types/argument.py

@@ -26,9 +26,9 @@ def type(self):
 
     def __eq__(self, other):
         return isinstance(other, Argument) and (
-            self.name == other.name,
-            self.type == other.type,
-            self.default_value == other.default_value,
+            self.name == other.name and
+            self.type == other.type and
+            self.default_value == other.default_value and
             self.description == other.description
         )