Add Python 3.7 test to Django 1.11

Author: benmurden

.travis.yml

@@ -23,6 +23,9 @@ env:
 matrix:
     fast_finish: true
     include:
+      - python: "3.7"
+        dist: xenial
+        env: DJANGO=1.11
       - python: "3.7"
         dist: xenial
         env: DJANGO=2.0