It is good practice to specify Maven plugins version explicitly. Since Maven 3, warnings are output when versions aren't specified. With BUILD-165, we've added a bunch a version, and since BUILD-169, we can enforce they're specified. Let's do this by adding the <requirePluginVersions> rule.

Worth noting for anyone stumbling upon this, or trying to test it:

• The enforcer plugin is bound to the validate phase of the default lifecycle.
• The clean lifecycle does not execute the validate phase
• Which means that mvn clean will not show up enforcer problems