Fix ReferenceError in init-ring-mqtt

[brian-mcnamara]

Issue when initializing which results in the error:

Saving state file /data/ring-state.json failed with error:
ReferenceError: systemId is not defined
    at main (file:///app/ring-mqtt/init-ring-mqtt.js:83:47)

[brian-mcnamara]

Github edit, I can add the new line back if desired.

[tsightler]

Thanks for the PR. I actually caught this about a week ago and fixed it in my local instance, but haven't pushed those changes to the dev branch yet. Since you went through the trouble to submit a PR, I'll merge it. Thanks!

[brian-mcnamara]

Thanks! I figured it was probably known, but it was easy enough to fix and submit.
And thank you for all your work on this project, it's been a great (and easy) integration between ring and HA.

[Scope666]

I'll second that, this is one of my favorite integrations!