Fix "Apache License, Version 2.0" spelling -- in pom.xml.template

There are many Java libraries licensed under "Apache License, Version 2.0" that do not use its official spelling.

This causes issues like https://issues.apache.org/jira/browse/MPIR-382: with every library defining its own spelling, it's difficult in large projects to have a clear view of all licenses in use.

Solr uses "Apache 2" instead of the official "Apache License, Version 2.0" spelling. ...in the pom.xml.template file used by the shadow maven build