Previously mocha, uglifyjs and jshint used when publishing a new version
were ensured / installed by `Rakefile` via the pre-commit git hook.
Those modules were automatically installed globally if not present in
`$PATH`.

Installing modules globally has one particular dowsides that we should
avoid: we can't ensure developers publishing new mustache.js versions
have the same version of these 3rd party modules installed.

If instead we make these modules local dev dependencies, we can ensure
which versions are installed, and we make 3rd party depedencies explicit
by listing them in `package.json`, rather than in `Rakefile`.