[fzf#vim#colors] Remove duplicate colorschemes (#278)

Use s:uniq() instead of uniq() for older versions of Vim.

We don't sort the list before passing it to s:uniq() because
1. s:uniq() can process unsorted lists.
2. And in that way, we can list color schemes from plugins before
   the default ones provided by Vim.

autoload/fzf/vim.vim

@@ -358,8 +358,8 @@ endfunction
 " ------------------------------------------------------------------
 function! fzf#vim#colors(...)
   return s:fzf('colors', {
-  \ 'source':  map(split(globpath(&rtp, "colors/*.vim"), "\n"),
-  \               "substitute(fnamemodify(v:val, ':t'), '\\..\\{-}$', '', '')"),
+  \ 'source':  s:uniq(map(split(globpath(&rtp, "colors/*.vim"), "\n"),
+  \               "substitute(fnamemodify(v:val, ':t'), '\\..\\{-}$', '', '')")),
   \ 'sink':    'colo',
   \ 'options': '+m --prompt="Colors> "'
   \}, a:000)