Fix cargo expand link in crate doc
diff --git a/src/lib.rs b/src/lib.rs
index fad1e45..2f05af3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -220,7 +220,7 @@
//! generated code looks like. Use `cargo rustc -- -Zunstable-options
//! --pretty=expanded` or the [`cargo expand`] subcommand.
//!
-//! [`cargo-expand`]: https://github.com/dtolnay/cargo-expand
+//! [`cargo expand`]: https://github.com/dtolnay/cargo-expand
//!
//! To show the expanded code for some crate that uses your procedural macro,
//! run `cargo expand` from that crate. To show the expanded code for one of