Replace deprecated OSGi plugin

[Capstan]

When running ./gradlew check --warning-mode all, there's the following output:

> Configure project :
The osgi plugin has been deprecated. This is scheduled to be removed in Gradle 6.0. Consider using the biz.aQute.bnd plugin instead.
        at build_dq0pen3kf87bpqz0v7n08tc3t.run(/…/github/java-json-tools/jackson-coreutils/build.gradle:23)

Replacing use of Gradle's deprecated OSGi Plugin
https://docs.gradle.org/5.0/userguide/osgi_plugin.html