upgrade to protobuf 4 #604
Description
- We've been getting build failures in this repo when we try upgrading protoc and/or protobuf-java to v4
- We have dependencies on grpc-java and scalapb which both still default to protobuf-java 3.
- scalapb 1.0.0 alpha support protobuf 4 #610 shows that we can get some of the way to supporting protobuf 4 but there are issues