Node express 跨域支持
app.all('*', function(req, res, next) {
    res.header('Access-Control-Allow-Origin', '*');
    res.header('Access-Control-Allow-Headers', 'Content-Type');
    res.header('Access-Control-Allow-Methods', '*');
    res.header('Content-Type', 'application/json;charset=utf-8');
    next();
});