Bump django from 3.0.7 to 3.1.3

Bumps [django](https://github.com/django/django) from 3.0.7 to 3.1.3.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@3.0.7...3.1.3)

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

Author: dependabot-preview[bot]

Pipfile.lock

@@ -1,6 +1,7 @@
-asgiref==3.2.10
-Django==3.1.2
-mysqlclient==2.0.1
-python-dotenv==0.15.0
-pytz==2020.1
-sqlparse==0.3.1
+-i https://pypi.org/simple/
+asgiref==3.3.1
+django==3.1.3
+mysqlclient==1.4.6
+python-dotenv==0.13.0
+pytz==2020.4
+sqlparse==0.4.1