travis: Add python 3.7 and upgrade deploy stage

Signed-off-by: Himanshu Sahdev aka CunningLearner <sahdev.himan@gmail.com>

Author: CunningLearner

.travis.yml

@@ -15,8 +15,11 @@ jobs:
     - python: 3.6
       env: TOXENV=py36
       name: "Python 3.6"
+    - python: 3.7
+      env: TOXENV=py37
+      name: "Python 3.7"
     - stage: deploy
-      python: 3.6
+      python: 3.7
       name: "Upload dev version to PyPi"
       script: ./.push-to-pypi.sh