CI for this repository isn't catching errors

[alexcrichton]

I first commited a bug in #37 which would cause the template to not build, but it was caught by @fitzgen's sharp eyes. Unfortunately though Travis didn't catch this.

The reason, I believe, is that cargo generate --git . --name testing, what Travis is currently doing, actually checks out the master branch of the repository rather than whatever branch the PR is set to be. This means that every PR is actually testing what's on master, not what's in the PR!