Nut, https://github.com/jingweno/nut, is a tool to manage Go dependencies and
versioning by vendorizing them, i.e. including them in your own repo.
This makes version management easier, as well as authenticating the contents of
this repository.
Also inthis change: Factor out the testing commands from .travis.yml to make it
easier to run them by hand. Add Vim swap files to .gitignore.