Update Ruby version to 1.9.3-p484

For consistency with other GDS repos so that we don't need to install
loads of versions of Ruby.
Tidy the {{ mustache }} publishing commit message
Update package.json for {{ mustache }} build

- Change description; I don't think this is temporary
- Add keywords
- Remove `main` and `scripts` that don't work
- Change author
- Remove nonexistent `readme`, `_id` and `_from` keys
Merge pull request #74 from alphagov/mustache-updates

{{ mustache }} updates