message: Fix a typo in the registries documentation.
diff: @@ -8,7 +8,7 @@ support publishing new crates directly from Cargo.
  > Note: If you are interested in mirroring or vendoring an existing registry,
  > take a look at [Source Replacement].
  -If you are implementing a registry server, see [Running at Registry] for more
  +If you are implementing a registry server, see [Running a Registry] for more
  details about the protocol between Cargo and a registry.
  ### Using an Alternate Registry
  @@ -99,7 +99,7 @@ token = "854DvwSlUwEHtIo3kWy6x7UCPKHfzCmy"
  ```
  [Source Replacement]: source-replacement.md
  -[Running at Registry]: running-a-registry.md
  +[Running a Registry]: running-a-registry.md
  [`cargo publish`]: ../commands/cargo-publish.md
  [`cargo package`]: ../commands/cargo-package.md
  [`cargo login`]: ../commands/cargo-login.md
  