Update tested Django releases

Drop Python 3.3 from tests, pytest doesn't support it anymore

.travis.yml

@@ -6,32 +6,25 @@ cache: pip
 
 python:
   - "2.7"
-  - "3.3"
   - "3.4"
   - "3.5"
   - "3.6"
 
 env:
   matrix:
-    - DJANGO=2.0
-    - DJANGO=1.8.18
-    - DJANGO=1.10.7
-    - DJANGO=1.11
+    - DJANGO=2.0.7
+    - DJANGO=1.8.19
+    - DJANGO=1.10.8
+    - DJANGO=1.11.14
 
 matrix:
   exclude:
     - python: "2.7"
-      env: DJANGO=2.0
-    - python: "3.3"
-      env: DJANGO=1.10.7
-    - python: "3.3"
-      env: DJANGO=1.11
-    - python: "3.3"
-      env: DJANGO=2.0
+      env: DJANGO=2.0.7
     - python: "3.6"
-      env: DJANGO=1.8.18
+      env: DJANGO=1.8.19
     - python: "3.6"
-      env: DJANGO=1.10.7
+      env: DJANGO=1.10.8
 
 install:
   - pip install -U Django==$DJANGO