Unprefix min-device-pixel-ratio

[nimbupani]

This needs to be done within the script to add prefixes. device pixel ratio applies not just for Webkit but for other rendering engines as well.

[benschwarz]

@miketaylr suggested I change the readme in reference to:
http://www.w3.org/blog/CSS/2012/06/14/unprefix-webkit-device-pixel-ratio

Any other hints to the unprefixing in practice?

[benschwarz]

https://developer.mozilla.org/en-US/docs/CSS/Media_queries states a bunch of media queries I've never heard of, including the unprefixable: min--moz-device-pixel-ration for Firefox before version 16!

This requires more R&D in respects to mobile editions of browsers.