环信REST API群组加人时报404，但是通过查询群组的API可以查到该Group ID

API路径：https://a1.easemob.com/hrsoft/ixuetong/chatgroups/80646901845721512/users
方法：POST
查询所有群聊接口关于该群聊的返回：
{ owner: 'hrsoft#ixuetong_555787ea305643a00481dc90',
  groupid: '80646901845721512',
  affiliations: 1,
  type: 'group',
  last_modified: '1436341870067',
  groupname: '55890258a25a341654cc7c0a:555787ea305643a00481dc90' }