use globby to resolve source files

[vbud]

Then we can hand gulp-purifycss an array of globs and negations like we do with gulp.src.

I ran into this because I was handing gulp-purifycss an array of values like this:

[
  'app/**/*.{js,html}',
  '!app/bower_components/**/*.{js,html}',
  '!app/**/*.spec.js'
]

And the negation wasn't working like it usually does with gulp.src, for example. So I looked into it and globby seemed to be the simplest way to achieve what I wanted.

My editor seems to have alphabetized the package.json file - the only changes there are to replace glob with globby and to bump the version to 0.2.1.