Added HSVA regex pattern.

This adds support for the `HSVA` color format. While editing color values in [Spectrum](https://github.com/bgrins/spectrum) I found that `HSVA` colors were showing up as invalid. This update fixes the issue.

Existing Code: <http://jsfiddle.net/neogeek/xmfdLmu9/>

With Pull Request Code: <http://jsfiddle.net/neogeek/xmfdLmu9/1>