Bump Django to latest 1.11.6

Django 1.11.6 was released on October 5, 2017.
We are still using 1.11 released on April 4, 2017.

Also bump all Django-related dependencies.

requirements.txt

@@ -6,14 +6,14 @@ celery==4.0.2
 coreapi==2.3.0
 coreschema==0.0.4
 dj-database-url==0.4.2
-Django==1.11
+Django==1.11.6
 django-appconf==1.0.2
-django-auth-ldap==1.2.15
+django-auth-ldap==1.2.16
 django-autocomplete-light==3.2.10
-django-compressor==2.1.1
-django-filter==1.0.2
+django-compressor==2.2
+django-filter==1.0.4
 django-jsonify==0.3.0
-django-polymorphic==1.2
+django-polymorphic==1.3
 djangorestframework==3.6.2
 gevent==1.2.1
 greenlet==0.4.12