Move graylog to dedicated repo
Move graylog to dedicated repo

The new repo uses gopkg.in for versioning.
This is the continuation of logrus moving hooks to dedicated repos.

The old repo
https://github.com/gemnasium/logrus-hooks/tree/master/graylog
is deprecated, as we don't want to share things there too (import
airbrake while I just want graylog). It will be removed in a few
months.

devopstaku/logrus