Revert "Update logstash_event gem to 1.2.02. We now default to the v1 format"

The logstash-event gem in version 1.2.x is not compatible with
Ruby 1.8 anymore which is currently a requirement for Rackstash.
As such, we have to use an older version.

This reverts commit 6ef0bfe5d659861a1a5ed2383a9f56543f4fc098.