Add error notifications for repository or organization owner

[electrum]

We had a typo in our contributors file which broke the CLA bot for us for several days. It would be nice if CLA bot could email us about such issues.

[ColinEberhardt]

Hi @electrum rather than sending emails, I've modified the bot so that it reports errors in the JSON configuration file via the GitHub build status.

You can see it in action here:

https://github.com/ColinEberhardt/cla-bot-playground/pull/3

If you look at the details of the failed status check, it clearly indicates that there is a configuration issue.

Hopefully this help.

(This fix has been deployed so is live now)