add coverage test to travis

.travis.yml

@@ -12,9 +12,10 @@ python:
 # command to install dependencies, e.g. pip install -r requirements.txt --use-mirrors
 install: 
     - "pip install -r requirements.txt"
+    - "pip install coverage"
     - "pip install coveralls"
 
 # command to run tests, e.g. python setup.py test
-script: python setup.py test
+script: coverage run --source=pipreqs setup.py test
 after_success:
     coveralls