Change <version.jboss.maven.plugin>7.3.Final to 7.4.Final

As per discussion at https://github.com/jboss-jdf/jboss-as-quickstart/pull/590#issuecomment-23262342

For "What's new" in 7.4 see https://issues.jboss.org/browse/JBASMP/fixforversion/12320400