fix: Update to latest throttling plugin

[playpauseandstop]

In attempt to fix unintentional retries on 422 error from GitHub,

1. Update to latest @octokit/plugin-throttling version
2. Depend on @octokit/plugin-retry plugin as well

Issue: #52

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I found it hard to find any other way to fix the original issue, so decided to update to latest throttling plugin (with updating config key) & include retry plugin as well.

My findings based on probot/probot@1a19bdd

If this is not expected solution for original issue, I'll need a help in fixing it.

Thanks

[softprops]

I think this change is useful but it will likely not fix the 422 error. GitHub returns these for invalid input https://developer.github.com/v3/#client-errors. Retrying on invalid input will likely not make the request more likely to succeed.

I'll merge this and take a deeper look.