Update ANTLR version

Current version of ANTLR in SystemML is v4.3.

When running SystemML on current Databricks Notebook via MLContext, we see this message:
"ANTLR Tool version 4.3 used for code generation does not match the current runtime version 4.5.1"

We can update ANTLR version in pom.xml from 4.3 to 4.5.1 (and run test suite to verify that nothing is broken). This has the benefits of moving us to a later version of ANTLR and should remove the ANTLR version messages when running in Databricks Notebook.