Only coverage report on test success, fixes nickmerwin#230

Addresses only the `jest` case, other cases can be handled via
subsequent pull requests.

README.md

@@ -56,7 +56,7 @@ env:
 - Use the following to run tests and push files to coveralls:
 
   ```sh
-  jest --coverage --coverageReporters=text-lcov | coveralls
+  jest --coverage && coveralls < coverage/lcov.info
   ```
 
 Check out an example [here](https://github.com/Ethan-Arrowood/harperdb-connect/blob/master/.travis.yml) which makes use of Travis CI build stages