Use cached Array.prototype.slice instead of [].slice

Because `Array.prototype.slice` works faster than `[].slice`.
(cf. http://jsperf.com/array-prototype-slice-call-vs-slice-call/7)

I think that in many cases this module is used repeatedly in a program such as [image-min](https://github.com/kevva/image-min) and its dependent [grunt-contrib-imagemin](https://github.com/gruntjs/grunt-contrib-imagemin).
So caching `Array.prototype.slice` will be effective in performance improvement.