1、咪咕管理后台用户留存记录（按天）查询优化，修复查看每月1号数据只有当月的缺陷；

app/admin/apis/migumanage/migu_admin.go

@@ -1577,7 +1577,7 @@ func (e MiGuDeployService) UserDayRetentionList(c *gin.Context) {
 	var dateList []string
 	if req.OnlyFirstDay {
 		// 每月1号
-		for date := nextMonth; !date.After(time.Now()); date = date.AddDate(1, 0, 0) {
+		for date := nextMonth; !date.After(time.Now()); date = date.AddDate(0, 1, 0) {
 			dateList = append(dateList, date.Format("2006-01-02"))
 		}
 	} else {