Automated integration tests against multiple webpack versions

[rmarscher]

This project would benefit from automated tests that could automatically run against different versions of webpack. Need to look into techniques for doing that. Any suggestions are welcome.

It looks like using environment variables and a script to install different dependencies based on the env var might work. Like this CakePHP plugin project does - https://github.com/FriendsOfCake/travis/blob/master/.travis.yml