wire antlr version 4.7.1

[frko]

It would be nice to upgrade to the latest generation runtime from antlr as it contains performance improvements and better error handling.

https://github.com/antlr/antlr4/releases/tag/4.6

[boris-petrov]

There is a version 4.7 now:

https://github.com/antlr/antlr4/releases/tag/4.7