Race-conditions with Issue Create

As expected, GitHub fires both an `issue_create` and `labeled` event (with the default label) immediately after each other.

Sometimes, the first event creates the issue for the second to reference.

Other times, both events cause the hook to lookup a non-existent story, create it, and now there are two.

Naturally, a job queue or a single server would resolve this, but I want to avoid too much complexity.

Since I'm using serverless (for now), this seems like a reasonable solution:
> https://serverless.com/blog/aws-lambda-sqs-serverless-integration/