Replace slf4j-simple with log4j-slf4j-impl (test dependency)
Replace slf4j-simple with log4j-slf4j-impl (test dependency)

Graylog2/log4j2-gelf,safetytrick/log4j2-gelf,aheusingfeld/log4j2-gelf,taulia/log4j2-gelf,michaelnielson-taulia/log4j2-gelf