Switch from 'minifier' to 'minify' for build minification (fixes #817)

This uses the 'minify' library (http://coderaiser.github.io/minify/), because the builds produced with 'minifier' (https://github.com/fizker/minifier) had a syntax error in Safari.

After merging this, you'll have to delete the `./node_modules` directory before running `npm install`. The command-line script in `./node_modoules/.bin/` has the same name as the previous one.