google-grpc-dev in buster

[Arnaud Rebillout <arnaud.rebillout@collabora.com>]

  Dear go devs,

I managed to build a package for docker v18.09.1 (which is the LTS for
docker), and I'd be happy to be able to have this package in time for
buster.

The main blocker on the way is `google-grpc-dev`:

- debian ships 1.11
- docker requires 1.12 and FTBFS otherwise
- salsa actually has the version 1.15 packaged, and docker builds just
fine against it.

I guess this package is important. I've seen that there are a lot of
reverse build deps.

My question: do you guys know what's blocking this package to 1.11? Is
there any chance to update it to 1.12, or will it break the whole
ecosystem??

Thanks!

  Arnaud