Remove Drive Name from Pathnames

This is a fix for building on Windows.
Jekyll would try to build `C:/…/_site/C:/index.html` (hence change to line 173)
Jekyll would build `C:/Documents and Settings/…/css-guru/Documents and Settings/…/css-guru/_site/css` (rebuilding entire directory tree within `pwd`). Removing the drive name from the pathname gets Ruby to build an absolute path instead of a relative path.

If you know a way to get the current drive's name instead of hardcoding "C:", please advise.