Logrus hook prints error if event has been dropped

[hnicke]

When using the logrus hook to send logs to sentry, the following line is printed everytime the hook is triggered but the event is dropped (e.g. by using BeforeSend):

Failed to fire hook: failed to send to sentry

The log is triggered by this particular error.
I think this error should not be thrown at all since it's a valid scenario to drop sentry events client-side.

[hnicke]

I have figured out that the error can be suppressed by setting a fallback:

hook.SetFallback(func(entry *log.Entry) error {
	return nil
})

Given this solution the PR is not needed anymore.

[cleptric]

We actually need to change this 😄
As said in the PR, the HttpTransport always returns an ID, regardless if the event was actually successfully submitted over the wire.