Generate function doesn't work on Mac

[skibblenybbles]

Due to a known issue in pyttsx3, the tts interpreter process hangs on .save_to_file() calls on recent Mac OS versions.

I tried the hack workarounds from the pyttsx3 community to no avail. The best solution would track down the source of the failure in the NSSS driver and fix it, but a decent workaround would just bypass pyttsx3 for the darwin platform and use the built-in say command.