Release stream tracks and close audioContext on stop recording in lam…

…ejs plugin (#197)

src/js/plugins/lamejs-plugin.js

@@ -54,6 +54,8 @@ class LamejsEngine extends RecordEngine {
         this.audioSourceNode.disconnect();
         this.processor.disconnect();
         this.processor.onaudioprocess = null;
+        this.inputStream.getAudioTracks().forEach(track => track.stop())
+        this.audioContext.close()
 
         this.engine.postMessage({cmd: 'finish'});
     }