Fix JsHintReporter _builtInIgnoreRegex

This is my first time to contribute to open source project. Everything to me is new. Like GitHub, git, VS SDK. Even I'm not good at Regex too. If I do anything wrong, please forgive me.

I just looking for #603, found JSHint ignore rule mention by @SLaks.
All '.' char in Regex require '\'.
I have tried to find a test case about this, but not exists. And I have no ability to create a new one. Hope this commit is right.