Upgrade to django 1.11.11

Update our dependencies as well to the latest stable version.
Signed-off-by: Jelle van der Waa <jelle@vdwaa.nl>

requirements.txt

 -e git+git://github.com/fredj/cssmin.git@master#egg=cssmin
-Django==1.8.18
+Django==1.11.11
 IPy==0.83
-Markdown==2.6.8
+Markdown==2.6.10
 MarkupSafe==0.23
 bencode==1.0
-django-countries==3.3
+django-countries==5.0
 jsmin==2.2.2
 pgpdump==1.5
-pytz>=2015.4
+pytz>=2017.3
 mock==2.0.0
 parse==1.8.2