Make golint pass an enable it in Travis to ensure the code remains consistent

[calavera]

- Do you want to request a feature or report a bug?

This is an enhancement to improve code quality.

- What is the current behavior?

Right now we're ignoring Go's linter rules.

- What is the expected behavior?

We should make sure the project passes the linter rules and enable make lint in Travis.

- Please mention your Go version, and operating system version.

Go 1.8 and up.