ci: merge travis matrix, add `salt-lint` & `rubocop` to `lint` job

[myii]

• Semi-automated using https://github.com/myii/ssf-formula/pull/60

[saltstack-formulas-travis]

:tada: This PR is included in version 0.3.1 :tada:

The release is available on GitHub release

Your semantic-release bot :package::rocket: