Compute coverage on Travis CI same as in tox (#88)

I want to know if my test suite is complete without the smoke test run.

.coveragerc

@@ -1,3 +1,6 @@
+[run]
+source = check_manifest
+
 [report]
 exclude_lines =
     pragma: nocover

.travis.yml

@@ -20,8 +20,9 @@ env:
 install:
     - pip install coverage coveralls mock flake8
 script:
-    - SKIP_NO_TESTS=1 coverage run --source=check_manifest setup.py test -q
-    - coverage run --source=check_manifest --append check_manifest.py
+    - SKIP_NO_TESTS=1 coverage run setup.py test -q
+    - coverage report -m
+    - python check_manifest.py
     - flake8 *.py
 after_script:
     - coveralls