[vim] Use fnameescape to escape command line arguments

Fix https://github.com/junegunn/fzf.vim/issues/404

Thanks to @janlazo.

plugin/fzf.vim

@@ -149,13 +149,8 @@ function! s:tmux_enabled()
 endfunction
 
 function! s:escape(path)
-  let escaped_chars = '$%#''"'
+  let path = fnameescape(a:path)
-
+  return s:is_win ? escape(path, '$') : path
-  if has('unix')
-    let escaped_chars .= ' \'
-  endif
-
-  return escape(a:path, escaped_chars)
 endfunction
 
 " Upgrade legacy options