emit vad event on partial transcript

lib/tasks/gather.js

@@ -430,6 +430,7 @@ class TaskGather extends Task {
         evt.alternatives[0].transcript.split(' ').length >= this.minBargeinWordCount) {
         if (!this.playComplete) {
           this.logger.debug({transcript: evt.alternatives[0].transcript}, 'killing audio due to speech');
+          this.emit('vad');
         }
         this._killAudio(cs);
       }