ci: Run builds against 3.5 & 3.6

- ctrl-c ctrl-v from Go
Signed-off-by: David Haynes <dhaynes3@gmu.edu>

.gitlab-ci.yml

@@ -15,5 +15,17 @@ whats-open-py2.7:
   type: test
   script:
     - python manage.py test
+
+whats-open-py3.5:
+  image: library/python:3.5
+  type: test
+  script:
+    - python manage.py test
+
+whats-open-py3.6:
+  image: library/python:3.6
+  type: test
+  script:
+    - python manage.py test
     - coverage run --source=website --omit=*migrations/*,*admin.py,*__init__.py,*.pyc manage.py test
     - coverage html -i && grep pc_cov htmlcov/index.html | egrep -o "[0-9]+\%" | awk '{ print "covered " $1;}'