Update travis config to only run deploy once (#837)

.travis.yml

@@ -12,8 +12,17 @@ after_success:
   - pip install coveralls
   - coveralls
 
-matrix:
+stages:
+  - test
+  - name: deploy
+    if: tag IS present
+
+jobs:
   fast_finish: true
+
+  allow_failures:
+    - env: DJANGO=master
+
   include:
     - python: 2.7
       env: DJANGO=1.11
@@ -56,10 +65,10 @@ matrix:
     - python: 3.7
       env: TOXENV=black,flake8
 
-  allow_failures:
-    - env: DJANGO=master
-
-deploy:
+    - stage: deploy
+      python: 3.7
+      after_success: true
+      deploy:
         provider: pypi
         user: syrusakbary
         on: