Simplify Velocity conditional for JUnit BOM dependency management

[behrangsa]

Replace #elseif version check with #else to apply JUnit BOM dependencyManagement for all non-JUnit 4 versions.

This change, makes the if conditions closer to and more consistent with archetype-resources/src/test/java/AppTest.java:

    #if ( $junitVersion == $null || $junitVersion.startsWith("4."))

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Addresses #128

[behrangsa]

I had previously signed the Apache Individual Contributor License Agreement when I contributed a PR to commons-io