Update MessageBuilder.php (#603)
Update MessageBuilder.php (#603)

预览群发消息时msgType改为mpvideo
overtrue/wechat,tianyong90/wechat,overtrue/wechat,acgrid/wechat,tianyong90/wechat,acgrid/wechat,allen05ren/wechat,ac1982/wechat,ac1982/wechat,hareluya/wechat,allen05ren/wechat