Upgrade Promise requirement

it has following fixes:
* Make Promise and Dataloader thread-safe syrusakbary/promise#81
* Fix memory leak on dynamically created types syrusakbary/promise#76
* and more https://github.com/syrusakbary/promise/releases

setup.py

@@ -85,7 +85,7 @@ def run_tests(self):
         'six>=1.10.0,<2',
         'graphql-core>=1.1,<2',
         'graphql-relay>=0.4.5,<1',
-        'promise>=2.0,<2.1',
+        'promise>=2.0,<2.4',
     ],
     tests_require=tests_require,
     extras_require={