updated default phpunit to be the one supplied by this task

I understand that you guys have removed third party dependencies like the composer installation of phpunit. But i think this task would be rather more useful if by default it shipped with a standalone phpunit.phar working version. As long as we state that on the readme like this ```This plugin comes with PHPUnit 3.7.19, but other versions can be installed.``` this way users can install other versions if they want to, but they will have all they need at start. I hope you guys consider this merge since it is very important for a grunt-init scaffold that our organization is building. 

By the way great job on this task it looks great :)