Bump django from 1.7 to 1.11.23

Bumps [django](https://github.com/django/django) from 1.7 to 1.11.23.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/1.7...1.11.23)

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/requirements.txt b/requirements.txt
index 3a89de4..ca10811 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,6 @@
 cffi==1.6.0
 cryptography==1.3.1
-Django==1.7
+Django==1.11.23
 django-axes==1.5.0
 django-custom-user==0.6
 django-extensions==1.6.1