Update msg.go (#958)

fix: send text message by api doesn't work. (#929)

internal/api/msg.go

@@ -170,7 +170,7 @@ func (m *MessageApi) getSendMsgReq(c *gin.Context, req apistruct.SendMsg) (sendM
 	log.ZDebug(c, "getSendMsgReq", "req", req.Content)
 	switch req.ContentType {
 	case constant.Text:
-		text, ok := req.Content["content"].(string)
+		text, ok := req.Content["text"].(string)
 		if !ok {
 			return nil, errs.ErrArgs.WithDetail("text is not string")
 		}