Check for formatting and lint errors in CI

[akshayjshah]

We should check for correctness using gofmt, govet, and golint as part of Travis builds. We already do this in the rest of the Fx-related OSS projects, so we should be able to just copy those bits of Makefile.

[akshayjshah]

Primary issue here is that the code in expand.go is all C-style and snake_case, so it doesn't pass our typical linter suite. We'll need to fix that file before we can move forward with this.

[akshayjshah]

Seems like this got done 🎉