golang protobuf bump

[kolyshkin]

README for https://github.com/golang/protobuf says:

It has been superseded by the google.golang.org/protobuf module, which contains an updated and simplified API, support for protobuf reflection, and many other improvements. We recommend that new code use the google.golang.org/protobuf module.

Versions v1.4 and later of github.com/golang/protobuf are implemented in terms of google.golang.org/protobuf. Programs which use both modules must use at least version v1.4 of this one.

Meaning we need to either switch to google.golang.org/protobuf, or at least use github.com/golang/protobuf v.1.4+.

[kolyshkin]

This needs to be coordinated with runc of course.

[kolyshkin]

Should be ixed by #38 and #43

[kolyshkin]

Tested with runc: opencontainers/runc#2807. Had to made a change for debug print of criu options as they are now represented slightly different (XXX_* are gone, all-lowercase are added).

@adrianreber can you please make a release?

[kolyshkin]

Since #46 we'll have to switch to v5 anyway, so maybe make a release once you merge it @adrianreber

[kolyshkin]

Fixed by #38 and #43, with #46 as a follow-up.