Bump django from 1.11.20 to 1.11.29 in /requirements

Bumps [django](https://github.com/django/django) from 1.11.20 to 1.11.29.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@1.11.20...1.11.29)

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

requirements/base.txt

@@ -1,4 +1,4 @@
-Django==1.11.20
+Django==1.11.29
 psycopg2==2.7.4
 Pillow==4.1.1
 python-memcached==1.58