Increased allowed version of aniso8601 (#1009)

Closes #1008 

The only change should not affect graphene https://bitbucket.org/nielsenb/aniso8601/issues/24/float-induced-rounding-errors-when-parsing

Author: Keats

setup.py

@@ -87,7 +87,7 @@ def run_tests(self):
         "six>=1.10.0,<2",
         "graphql-core>=2.1,<3",
         "graphql-relay>=2,<3",
-        "aniso8601>=3,<=6",
+        "aniso8601>=3,<=7",
     ],
     tests_require=tests_require,
     extras_require={