Update Vert.x to 3.9.0

RMB currently uses vert.x 3.8.5. The 3.8.x versions are out of support since the release of vert.x 3.9.0 on 2nd April 2020. We should use 3.9 for Goldenrod.

Most notable breaking change of 3.9 is the vertx-pg-client sql client query API that becomes fluent:

https://vertx.io/blog/eclipse-vert-x-3-9-0-released/
https://github.com/vert-x3/wiki/wiki/3.9.0-Deprecations-and-breaking-changes#fluent-query-api

3.8: client.query(sql, ar -> ...);
3.9: client.query(sql).execute(ar -> ...);

3.8: client.preparedQuery(sql, tuple, ar -> ...);
3.9: client.preparedQuery(sql).execute(tuple, ar -> ...);

3.8: client.preparedBatch(sql, listOfTuples, ar -> ...);
3.9: client.preparedQuery(sql).executeBatch(listOfTuples, ar -> ...);