[vim] fzf#exec: Shell-escape fzf binary path

Fix #2877

plugin/fzf.vim

@@ -164,7 +164,7 @@ function s:get_version(bin)
   if has_key(s:versions, a:bin)
     return s:versions[a:bin]
   end
-  let command = a:bin . ' --version --no-height'
+  let command = fzf#shellescape(a:bin) . ' --version --no-height'
   let output = systemlist(command)
   if v:shell_error || empty(output)
     return ''