Fix the lack of coverage report on coveralls.io

It turns out the docs target cleans out the environment before it does
its thing, which results in a deleted coverage report file.

Coveralls gets v angry in this situation.

.travis.yml

@@ -17,13 +17,16 @@ install:
   - ./env/bin/pip install coveralls
 
 script:
+  - 'make docs'
   - make checkstyle
   - make test
-  - make docs
 
 after_success:
   - ./env/bin/coveralls
 
+before_deploy:
+  - 'make docs'
+
 deploy:
 - provider: pypi
   user: marvinpinto