This changes the pre-commit hook that we've used for years to keep the
version value found in `package.json` in sync with the one in
`mustache.js`, to change `mustache.mjs` instead since that's where the
source code lives now.

[spm](https://github.com/spmjs/spm) seems to have been stale for 4 years
and has a deprecation warning in its github repository.

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 downside 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 dependencies explicit by listing them in `package.json`, rather than in `Rakefile`.

:v: colorified
https://github.com/janl/mustache.js/issues/462

:v: Add empty line between variables and loop, Change "executing" to "Installing", Add new line at the end of the last echo
https://github.com/janl/mustache.js/issues/462

:v: Removed trailing \n, echo changed for if
https://github.com/janl/mustache.js/issues/462

:v: added the word backup into the text.
https://github.com/janl/mustache.js/issues/462

Modified echo text
https://github.com/janl/mustache.js/issues/462

`version` is currently a moot prop since git tags are used instead. More
info at https://github.com/bower/bower.json-spec/commit/a325da3.

Due to eslint changes, pre-commit hook was failing to locate version in
mustache.js due to code using single quotes now, therefore "X.X.X" was
not longer matching, and had to be changed to 'X.X.X'.