Make the build reproducible

This bumps to pom-fiji 5.0.4, which upgrades the imagescience component
to 2.4.2, its first non-tainted release.

It eliminates the following error:

    $ mvn org.scijava:scijava-maven-plugin:0.3.0:verify-no-snapshots
    [ERROR] Found SNAPSHOT parent:
            sc.fiji:pom-fiji-plugins:2.0.0-SNAPSHOT
            sc.fiji:imagescience:2.4.1
            sc.fiji:Trainable_Segmentation:2.1.4-SNAPSHOT