Escaping spaces in rgb_colors path

[dandesousa]

What

• Escapes special characters in filenames when resolving rgb_colors bundle sub-directory

Why

• On cygwin, I was installing my bundles and noticed that vim complains with the following error on install / first open:

E172: Only one file name allowed: source /home/Daniel DeSousa/.vim/bundle/desert-warm-256/colors/rgb_colors

It seems to be caused by the space in my home directory as auto-generated by cygwin to match my NT user.

I haven't tested this on my other environments but the command should be safe.