Bump 'mincer' and 'source-map' modules for 'larasset-js'.

Because 'source-map' 0.1.35 and 0.1.36 are buggies and 'mincer' 1.1.2
supports Source Mapping for Firefox.

So if you have already installed Larasset, you need to run this two
commands:
npm uninstall -g larasset-js
npm install -g vendor/efficiently/larasset