pom: update to oncrpc4j-2.3.1

Changelog for oncrpc4j-2.3.0..oncrpc4j-2.3.1
    * [a3c4887] portmap: add OncRpcEmbeddedPortmap#shutdown()

Acked-by: Gerd Behrmann
Target: master, 0.9, 0.8
(cherry picked from commit 66c91af5fcd388efe1c51f5573c7e823b79162cb)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>