Fix protobuf dependency invalid semver for cargo 1.54 for v0.5.x

[jeanphilippeD]

With this, https://github.com/rust-lang/cargo/pull/9508, the dependency can no longer be used. What was picked with 1.53 cargo was ~2.0, so use that instead.

This needs to be a new branch 0.5.1 that I branched from tag v0.5.0

Test: Verify dependency can now be used. protobuf in cargo.lock is unchanged in my dependent project.

[BusyJay]

You need to sign off your commits.

[jeanphilippeD]

Thanks, Added the sign off line in the commit now.