Bump html-minifier

Hi.

Thank you very much for jstfiy. It was pretty useful to me.

We needed one feature that was new in 0.6.0, so I've updated the dependency. I hope is OK for you. The version seemed 100% compatible as per the changelog, and the tests passing, and my own setup working.

I've also fixed the require() call to one that uses the proper naming (in the tests). I guess you ran it on a Windows filesystem, where the case is preserved, but not enforced.

Thank you.