Tienes que descargarte estas librerias:
http://www.slf4j.org/download.html
La documentacion dice: "... placing one (and only one) of slf4j-nop.jar, slf4j-simple.jar, slf4j-log4j12.jar, slf4j-jdk14.jar or logback-classic.jar on the class path should solve the problem ..."
saludos!