To resolve this, we need to update `Cargo.lock`. Luckily, cargo provides a
command to do this easily.
-First, go into the `src/` directory since that is where `Cargo.toml` is in
-the rust repository. Then run, `cargo update -p rustfmt-nightly` to solve
-the problem.
-
```
-$ cd src
$ cargo update -p rustfmt-nightly
```
-This should change the version listed in `src/Cargo.lock` to the new version you updated
+This should change the version listed in `Cargo.lock` to the new version you updated
the submodule to. Running `./x.py build` should work now.
## Writing Documentation