Update the base image from jessie to stretch (for parity with the Java).
Update the base image from jessie to stretch (for parity with the Java).

Add Maven and OpenJDK 8 and add JRuby 9.2.x and 9.3.x.

Replace keys.gnupg.net with keyserver.ubuntu.com as the GPG keyserver since the former no longer exists.

google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf