- Contains the revert to [rust 2018](https://github.com/hyperium/tonic/pull/847).
- Bumps both tonic and tonic-build.
- tonic-build goes from 0.6.0 to 0.6.2 since there was no 0.6.1. I
  believe we want tonic and tonic-build versions to follow each other.