Updated composer.json
Updated composer.json

This fork is now the official library. Renamed package to
graylog2/gelf-php

Gummibeer/gelf-php,practo/gelf-php,verschoof/gelf-php,JeroenDeDauw/gelf-php,proximedia/gelf-php,zhdanovartur/gelf-php,bzikarsky/gelf-php