support all versions of django 1.11 (#674)

Author: rib3

contrib/opencensus-ext-django/setup.py

@@ -39,7 +39,7 @@
     include_package_data=True,
     long_description=open('README.rst').read(),
     install_requires=[
-        'Django >= 1.11.0, <= 1.11.20',
+        'Django >= 1.11.0, < 1.12.0',
         'opencensus >= 0.7.dev0, < 1.0.0',
     ],
     extras_require={},