Raise errors if webhooks are run out of order. This will trigger Sidekiq retries.

Signed-off-by: David Celis <me@davidcel.is>
Have Webhooks raise errors if run out of order

There can be potential ordering errors if webhook requests are received
out of order. It's best to, if one of these conditions is met, simply
raise an error from the worker. This will trigger a Sidekiq retry.

Signed-off-by: David Celis <me@davidcel.is>