`resolver = "3"` not supported when publishing packages

[LawnGnome]

From Zulip:

error: failed to publish to registry at https://crates.io

Caused by:
  the remote server responded with an error (status 400 Bad Request): failed to parse `Cargo.toml` manifest file

  TOML parse error at line 37, column 12
     |
  37 | resolver = "3"
     |            ^^^
  unknown variant `3`, expected `1` or `2`

[LawnGnome]

Root cause should be LukeMathWalker/cargo-manifest#63.