Packaging for gom - a Go dependency manager

https://github.com/mattn/gom

Package is named golang-gom because there's an existing unrelated
package called gom in Ubuntu.

The version number was generated by tagging the first commit in the
upstream repo as '0', and then running `git describe`.
Merge pull request #77 from alphagov/gom

Packaging for gom - a Go dependency manager