Updated requirements to use graphql-core >= 2.1

Author: syrusakbary

graphene/__init__.py

@@ -42,7 +42,7 @@
 from .utils.module_loading import lazy_import
 
 
-VERSION = (2, 1, 2, "final", 0)
+VERSION = (2, 1, 3, "final", 0)
 
 __version__ = get_version(VERSION)
 

graphene/pyutils/compat.py

@@ -2,10 +2,7 @@
 
 import six
 
-try:
-    from enum import Enum
-except ImportError:
-    from .enum import Enum
+from graphql.pyutils.compat import Enum
 
 try:
     from inspect import signature