Does not take into account max post size

[alistairreynolds]

For errors that exceed that max allowed size on airbrake, it doesn't truncate the data and silently fails.

This seems to happen when there's a stack of errors that try to get reported at once.

Instead silently failing so that the error never gets discovered, it should truncate the error like in the airbrake/airbrake repo below:

airbrake/airbrake#626