[vim] Improve `strip_trailing_whitespaces`
[vim] Improve `strip_trailing_whitespaces`

Add `markdown` to the `excludedFileTypes` array as 'mkd.markdown'
doesn't always work.

wingy3181/dotfiles,zlot/dotfiles,makabde/dotfiles,christophermoura/dotfiles,christophermoura/dotfiles,oddlord/dotfiles,b-boogaard/dotfiles,AlbertoElias/dotfiles,girishramnani/dotfiles,wingy3181/dotfiles,zlot/dotfiles,newtonne/dotfiles,girishramnani/dotfiles,EDiLD/dotfiles,mickael83/ubuntu-dotfiles,wingy3181/dotfiles,newtonne/dotfiles,pbrooks/dotfiles,AlbertoElias/dotfiles,mickael83/ubuntu-dotfiles,makabde/dotfiles,EDiLD/dotfiles