pom-scijava: bump the version of the imagej-maven-plugin to use

This version has two improvements over the old one: it no longer
complains about unset imagej.app.directory for projects that clearly
do not have ImageJ 1.x as dependency, and it warns after copying
artifacts when there are potentially-incompatible versions lying
about in the target directory (and the plugin can be configured to
delete them instead, too).

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