Fix coveralls report generation

.travis.yml

@@ -29,14 +29,15 @@ install:
     - pip install -U pip
     - pip install -U -r requirements.txt -r requirements-dev.txt .
     - |
+        # Overwrite twisted package for test
         set -e
         [ $TWISTED = latest ] || pip install Twisted==$TWISTED
-    - pip install -U tox coveralls
+    - pip install -U tox coveralls coverage
 
 # command to run tests
 script:
     - trial txrwlock
-    - trial --coverage txrwlock
+    - coverage run --branch --source=txrwlock $(which trial) txrwlock && coverage report -m
     - python setup.py build_sphinx
 
 after_success: