Fix invalid pom.xml in optaweb-vehicle-routing-backend

There is invalid pom.xml for org/optaweb/vehiclerouting/optaweb-vehicle-routing-backend/7.33.0.Final-redhat-00002/optaweb-vehicle-routing-backend-7.33.0.Final-redhat-00002.pom

The error says: cvc-complex-type.3.2.2: Attribute 'combine.self' is not allowed to appear in element 'configuration'.

It is related to this part which is not allowed by the XSD (but can be done at the child elements, according to the XSD):

<configuration combine.self="override">

The above construct works in Maven, despite it is not allowed by the XSD.

[1] http://maven.apache.org/xsd/maven-4.0.0.xsd

Reference to documentation is at http://maven.apache.org/pom.html#Plugins and the solution is to move this attribute to child element in configuration.