Increasing the needed version of django-filter

setup.py

@@ -17,7 +17,7 @@ setup(name='political-memory',
         'django-coffeescript>=0.7,<0.8',
         'django-compressor>=1,<2',
         'django-datetime-widget>=0.9,<1.0',
-        'django-filter>=0.13,<0.14',
+        'django-filter>=0.15,<0.16,
         'django-fontawesome>=0.2,<0.3',
         'django-rql-filter>=0.1.3,<0.2',
         'django-taggit>=0.17,<0.18',