Clear message on retry

Close #459

plug.vim

@@ -660,7 +660,7 @@ function! s:switch_out(...)
 endfunction
 
 function! s:finish_bindings()
-  nnoremap <silent> <buffer> R  :silent! call <SID>retry()<cr>
+  nnoremap <silent> <buffer> R  :call <SID>retry()<cr>
   nnoremap <silent> <buffer> D  :PlugDiff<cr>
   nnoremap <silent> <buffer> S  :PlugStatus<cr>
   nnoremap <silent> <buffer> U  :call <SID>status_update()<cr>
@@ -812,6 +812,7 @@ function! s:retry()
   if empty(s:update.errors)
     return
   endif
+  echo
   call s:update_impl(s:update.pull, s:update.force,
         \ extend(copy(s:update.errors), [s:update.threads]))
 endfunction