Consequences of Apache parent POM v18

[Andy Seaborne <an...@apache.org>]

On upgrading the Apache parent POM (it drives the ASF release process on 
top of the the release plugin) to v18, jena-maven-tools breaks [*].

The problem is there at v17 as well.

We had been using v16 up to Jena 3.1.0.

I've run out of ideas as to what this is so, with regret, I've left the 
jena-maven-tools out of the main build.

Going back to v16 is possible but feels like saving trouble up for the 
future.

	Andy

[*]

[ERROR] Failed to execute goal 
org.apache.maven.plugins:maven-plugin-plugin:3.4:helpmojo (help-goal) on 
project jena-maven-tools: Execution help-goal of goal 
org.apache.maven.plugins:maven-plugin-plugin:3.4:helpmojo failed: syntax 
error @[45,42] in 
file:/home/afs/Jena/jena-maven-tools/src/main/java/org/apache/jena/tools/schemagen/SchemagenOptions.java 
-> [Help 1]