Use ${nar.groupId}

This is necessary because nar-maven-plugin's groupId had to be changed
to conform with the requirements of Maven plugins: only core Maven
plugins are allowed to have org.apache.maven.plugins as groupId, and
unfortunately, core Maven prefers the quite limited maven-native-plugin
noone is using.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Bump parent POM to use current nar-maven-plugin

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>