depedency - remove Modernizr extras, Lodash 'isUndefined'

Don't need the Modernizr extras for this plugin, and I've stopped using
the Lodash call to 'isUndefined'. (It would be very handy for
grunt-lodash to do this for me...)

This commit reduces the final plugin size by:

- original: 10%, to 88KB
- minified: 21%, to 23KB
- minified + gzipped: 22%, to 5KB