Upgrade protobuf-java to 3.7.1
Upgrade protobuf-java to 3.7.1

In change Ic8fa455e8, rules_closure was updated to a version that
depends on protobuf 3.7.1. Update the version used in Gerrit to the
same version.

This version also fixes an illegal reflective access warning in JDK 9+.

Change-Id: Idb9403165ed65b9219d095e0fdbbe4646771e20a

GerritCodeReview/gerrit,qtproject/qtqa-gerrit,WANdisco/gerrit,WANdisco/gerrit,WANdisco/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit,WANdisco/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit,qtproject/qtqa-gerrit,qtproject/qtqa-gerrit,qtproject/qtqa-gerrit,GerritCodeReview/gerrit,WANdisco/gerrit,qtproject/qtqa-gerrit,WANdisco/gerrit,GerritCodeReview/gerrit,WANdisco/gerrit,GerritCodeReview/gerrit