travis ci pip version changed.

Author: shashankaryan

.travis.yml

@@ -12,7 +12,7 @@ cache:
   - $HOME/.pip-cache/
 
 install:
-  - pip install pip==8.1.2
+  - pip install pip==9.0.1
   - pip install -r requirements-dev.txt --allow-all-external
   - pip install coveralls