[Java] Update hello-world org.slf4j artifacts to 1.7.28
[Java] Update hello-world org.slf4j artifacts to 1.7.28

* hello-world example intentionally contains direct artifact
  version numbers

bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr