Should SpeechRecognition fire an error event in case of microphone permission denial

[youennf]

According https://webaudio.github.io/web-speech-api/#start-session-algorithm, microphone permission is requested in step 5.
If denied, the steps are aborted.

I would have thought that an error event handler would have been fired.

[evanbliu]

Good catch! I've sent out PR #166 to fix this.