StaticLoggerBinder#REQUESTED_API_VERSION is set to 1.7.16 in Version 1.1.7, but should be set to 1.7.20 as declared in the compile dependencies on http://mvnrepository.com/artifact/ch.qos.logback/logback-classic/1.1.7

This leads to the following logfile entry on every start:
SLF4J: The requested version 1.7.16 by your slf4j binding is not compatible with [1.6]
SLF4J: See http://www.slf4j.org/codes.html#version_mismatch for further details.

How the version check of SLF4J works is documented in: http://www.slf4j.org/faq.html#version_checks