release-version.sh: update ImageJ2 root POM name

It was changed from "pom-ij-base" to "pom-imagej" to match
related projects (e.g., "pom-imglib2" and "pom-scifio"); see:

https://github.com/imagej/imagej/commit/95c14f715590e4033b05c2bdef720516bcd1e9c0