fix bug for spawn args wrong position

based on http://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options

args(eg: --debug=port) should be first element in the options array.

this pull request will fix a bug mentioned at http://nodejs.netease.com/topic/515251b97f53b3d3330025c7#519eff6a3e8b1fca031b90f1