Increase the allowed version of aniso8601 (#1072)

Author: ymoch

setup.py

@@ -82,7 +82,7 @@ def run_tests(self):
     install_requires=[
         "graphql-core>=3.0.0a0,<4",
         "graphql-relay>=3.0.0a0,<4",
-        "aniso8601>=6,<8",
+        "aniso8601>=6,<9",
     ],
     tests_require=tests_require,
     extras_require={"test": tests_require},