sysutils/rubygem-fluent-plugin-graylog: update to version 1.0.2

Make the port build with a modern version of rubygem-fluentd. fluentd
claims to be backwards compatible, so the dependency on 0.12.36 seems
too narrow. Allow building with any version > 0.12.36.

This software is orphaned upstreams, so expire the port in two months.