Bump django from 3.1 to 3.1.6

Bumps [django](https://github.com/django/django) from 3.1 to 3.1.6.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@3.1...3.1.6)

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -4,10 +4,17 @@
 #
 #    pip-compile --output-file=requirements.txt
 #
-asgiref==3.2.10           # via django
-bump2version==1.0.0       # via bumpversion
+asgiref==3.2.10
+    # via django
+bump2version==1.0.0
+    # via bumpversion
 bumpversion==0.6.0
+    # via -r requirements.in
 coverage==5.2.1
-django==3.1
-pytz==2020.1              # via django
-sqlparse==0.3.1           # via django
+    # via -r requirements.in
+django==3.1.6
+    # via -r requirements.in
+pytz==2020.1
+    # via django
+sqlparse==0.3.1
+    # via django