`onend` event don't work on Safari

[alexlana]

Is your feature request related to a problem? Please describe.
The end event is messy in Safari.

Describe the solution you'd like
By adding window. before the variable utterance it works perfectly in Safari.

I worked on it in a fork, if you think it can be helpful, I will love to contribute.

[jankapunkt]

Hey @alexlana thank your for reporting. Can you please specify the line of the code, where utterance exists? => https://github.com/jankapunkt/easy-speech/blob/master/src/EasySpeech.js

Of course, I would be very pleased to see a pull request on this.

[jankapunkt]

@alexlana where do you actually put window in front of utterance?