Allow define options for colors

[estevejm]

From PHPUnit 4.4 colors output was modified to only output colors when executed from terminal (PR), so this task doesn't display colors for versions 4.4 and 4.5 (current stable version).

For 4.6 (current beta) support for colors options has been added (PR), so we can force to output colors when running PHPUnit from Grunt.

We need to give support to the options colors to have the parameters "never", "auto" and "always".

Maybe a good solution would be to keep with the boolean flag in the grunt-phpunit task but with the following map:

• colors: false adds the option --colors=never
• colors: true adds the option --colors=always

This should be enough for us, "auto" and "never" has the same outcome.

[AchoArnold]

+1 for this. Any walkarounds @estevejm?