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

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

.salt-lint

@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-
+# vim: ft=yaml
+---
+exclude_paths: []
+skip_list:
+  # Using `salt-lint` for linting other files as well, such as Jinja macros/templates
+  - 205  # Use ".sls" as a Salt State file extension
+  # Skipping `207` and `208` because `210` is sufficient, at least for the time-being
+  # I.e. Allows 3-digit unquoted codes to still be used, such as `644` and `755`
+  - 207  # File modes should always be encapsulated in quotation marks
+  - 208  # File modes should always contain a leading zero
+tags: []
+verbosity: 1