ISIS-501: Maven error with DN enhancer: required artifact missing 

Seems that there has been changes on the DN repositories and/or
dependencies recently. 

The solution is to go to the pom.xml of the "dom" (domain) module and
force the "datanucleus-maven-plugin" to use the jdo-api 3.0.1 version,
instead of the 3.0.1-SNAPSHOT version.


Signed-off-by: Óscar Bou <o.bou@gesconsultor.com>