Update django from 3.1rc1 to 3.1

Author: pyup-bot

requirements.txt

@@ -5,7 +5,7 @@ attrs==19.3.0
 black==19.10b0
 click==7.1.2
 coverage==5.2.1
-Django==3.1rc1
+Django==3.1
 django-cors-headers==3.4.0
 django-filter==2.3.0
 djangorestframework==3.11.0