fix problem with compiled slf4j version

[marwin1991]

https://github.com/logchange/hofund/blob/master/hofund-core/pom.xml

  Caused by: java.lang.UnsupportedClassVersionError: org/slf4j/Logger has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0 (unable to load class [org.slf4j.Logger])


[INFO] \- dev.logchange.hofund:hofund-core:jar:0.6.0:compile
[INFO]    \- org.slf4j:slf4j-api:jar:2.1.0-alpha0:compile (version selected from constraint [1.7.28,))