Move to official major Python 3.9 in Travis (#847)

Author: sliverc

Diff for: .travis.yml

@@ -63,19 +63,20 @@ matrix:
     - python: 3.8
       env: TOXENV=py38-django31-drfmaster
 
-    - python: 3.9-dev
+    - python: 3.9
       env: TOXENV=py39-django22-drf312
-    - python: 3.9-dev
+    - python: 3.9
       env: TOXENV=py39-django22-drfmaster
-    - python: 3.9-dev
+    - python: 3.9
       env: TOXENV=py39-django30-drf312
-    - python: 3.9-dev
+    - python: 3.9
       env: TOXENV=py39-django30-drfmaster
-    - python: 3.9-dev
+    - python: 3.9
       env: TOXENV=py39-django31-drf312
-    - python: 3.9-dev
+    - python: 3.9
       env: TOXENV=py39-django31-drfmaster
 
+
 install:
   - pip install tox
 script: