Fix GraphQL-core dependency

GraphQL-core released `3.2.0rc1` with some breaking changes and
1. We should be getting RC releases in our dependencies
2. It has breaking changes, so we shouldn't get 3.2.0 unless someone fixes it explicitly

Author: ekampf

setup.py

@@ -82,7 +82,7 @@ def run_tests(self):
     keywords="api graphql protocol rest relay graphene",
     packages=find_packages(exclude=["examples*"]),
     install_requires=[
-        "graphql-core>=3.1.2,<4",
+        "graphql-core~=3.1.2",
         "graphql-relay>=3.0,<4",
         "aniso8601>=8,<10",
     ],