don't restrict version number for the iso8601 package

Author: jdugan1024

setup.py

@@ -57,7 +57,7 @@ def run_tests(self):
         'six>=1.10.0',
         'graphql-core>=0.4.9',
         'graphql-relay==0.3.3',
-        'iso8601==0.1.11',
+        'iso8601',
     ],
     tests_require=[
         'django-filter>=0.10.0',