code: func (wxa *MiniProgram) GetAnalysisMonthlyRetain(beginDate, endDate string) (result ResAnalysisRetain, err error) {
  	return wxa.getAnalysisRetain(getAnalysisMonthlyRetainURL, beginDate, endDate)
  }
docs: // GetAnalysisMonthlyRetain 获取用户访问小程序月留存