Fix memory leak when creating audio CMSampleBuffer #86

Author: hiroshihorie

sdk/objc/api/peerconnection/RTCAudioTrack.mm

@@ -151,6 +151,9 @@ void OnData(const void *audio_data,
                                   0,
                                   NULL,
                                   &buffer);
+    // format is no longer required
+    CFRelease(format);
+
     if (status != 0) {
       NSLog(@"RTCAudioTrack: Failed to allocate sample buffer");
       return;