Adding more python versions to test matrix

.travis.yml

@@ -1,6 +1,8 @@
 sudo: false
 language: python
 python:
+  - 3.8
+  - 3.7
   - 3.6
   - 3.5
   - 2.7
@@ -49,7 +51,7 @@ deploy:
   on:
     tags: true
     condition: $DJANGO = '>=2.0,<2.1'
-    python: 3.6
+    python: 3.8
     repo: etianen/django-watson
 notifications:
   email: false