修正 gcc 4.8 下编译问题

webrtc/WebRtcTransport.cpp

@@ -385,10 +385,10 @@ void WebRtcTransportImp::onStartWebRTC() {
         _ssrc_to_track[track->offer_ssrc_rtx] = track;
 
         //rtp pt --> MediaTrack
-        _pt_to_track.emplace(track->plan_rtp->pt, new WrappedRtpTrack(track, _twcc_ctx, *this));
+        _pt_to_track.emplace(track->plan_rtp->pt, std::unique_ptr<WrappedMediaTrack>(new WrappedRtpTrack(track, _twcc_ctx, *this)));
         if (track->plan_rtx) {
             //rtx pt --> MediaTrack
-            _pt_to_track.emplace(track->plan_rtx->pt, new WrappedRtxTrack(track));
+            _pt_to_track.emplace(track->plan_rtx->pt, std::unique_ptr<WrappedMediaTrack>(new WrappedRtxTrack(track)));
         }
         if (m_offer->type != TrackApplication) {
             //记录rtp ext类型与id的关系，方便接收或发送rtp时修改rtp ext id