Bumped Django to resolve CVE-2020-7471 (#3126)

Author: jackton1

kubernetes_engine/django_tutorial/requirements.txt

@@ -1,6 +1,6 @@
 Django==3.0.2; python_version > '3.5'
 Django==2.2.9; python_version == '3.5'
-Django==1.11.27;python_version < '3.0'
+Django==1.11.28;python_version < '3.0'
 # Uncomment the mysqlclient requirement if you are using MySQL rather than
 # PostgreSQL. You must also have a MySQL client installed in that case.
 #mysqlclient==1.4.1