The plugin should be marked to be thread safe

[khmarbaise]

If you start a build which contains antlr4test-maven-plugin with multi thread support (parallel build) you get the following warning:

[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ cql ---
[INFO] Building jar: ..../grammars-v4/cql/target/cql-1.0-SNAPSHOT.jar
[INFO] 
[INFO] ----------------------< org.antlr.grammars:cql3 >-----------------------
[INFO] Building Apache Cassandra CQL 3 grammar 1.0-SNAPSHOT            [34/256]
[INFO] --------------------------------[ jar ]---------------------------------
[WARNING] *****************************************************************
[WARNING] * Your build is requesting parallel execution, but project      *
[WARNING] * contains the following plugin(s) that have goals not marked   *
[WARNING] * as @threadSafe to support parallel building.                  *
[WARNING] * While this /may/ work fine, please look for plugin updates    *
[WARNING] * and/or request plugins be made thread-safe.                   *
[WARNING] * If reporting an issue, report it against the plugin in        *
[WARNING] * question, not against maven-core                              *
[WARNING] *****************************************************************
[WARNING] The following plugins are not marked @threadSafe in Apache Cassandra CQL 3 grammar:
[WARNING] com.khubla.antlr:antlr4test-maven-plugin:1.17
[WARNING] org.antlr:antlr4-maven-plugin:4.9.1
[WARNING] Enable debug to see more precisely which goals are not marked @threadSafe.
[WARNING] *****************************************************************
[INFO] 
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ cql3 ---

It would be nice to mark the antlr4-maven-plugin threadSafe = true to suppress this warning.