Try different coveralls library

.travis.yml

@@ -8,7 +8,7 @@ python:
 install:
   - python setup.py -q install
   - pip install pytest-cov
-  - pip install python-coveralls
+  - pip install coveralls
 script:
   - py.test tests.py --cov jsonref --cov proxytypes --cov-report term-missing
   # Docs are in python 3 format