Pin graphql-core to <3

Author: jkimbo

setup.py

@@ -21,8 +21,8 @@
     keywords='api graphql protocol aiohttp',
     packages=find_packages(exclude=['tests']),
     install_requires=[
-        'graphql-core>=2.0.dev',
-        'graphql-server-core>=1.0.dev',
+        'graphql-core>=2.0.dev,<3',
+        'graphql-server-core>=1.0.dev,<2',
         'aiohttp>=2.0.0',
         'pytest-runner',
     ],