Use browser-launcher2.

I've kinda just changed this with a quick fix to make it work for me, I'll probably just bundle it into my app if you don't accept this, so whatever. [browser-launcher2](https://github.com/benderjs/browser-launcher2) resolves the aforementioned [browsers not closing on OS X](https://github.com/substack/browser-launcher/issues/34) issue.

[browser-launcher2](https://github.com/benderjs/browser-launcher2) (in yellow) also seems to have far more activity.

![image](https://cloud.githubusercontent.com/assets/43438/4502737/04d97b76-4acd-11e4-9d62-dbcd2bc4c67f.png)

![image](https://cloud.githubusercontent.com/assets/43438/4502720/c719d0ec-4acc-11e4-91cd-c96f63873d13.png)