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.