Update visit-mut feature in crate-level doc
diff --git a/src/lib.rs b/src/lib.rs
index 952af8e..e6e08e0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -247,7 +247,7 @@
//! - **`printing`** *(enabled by default)* — Ability to print a syntax tree
//! node as tokens of Rust source code.
//! - **`visit`** — Trait for traversing a syntax tree.
-//! - **`visit_mut`** — Trait for traversing and mutating in place a syntax
+//! - **`visit-mut`** — Trait for traversing and mutating in place a syntax
//! tree.
//! - **`fold`** — Trait for transforming an owned syntax tree.
//! - **`clone-impls`** *(enabled by default)* — Clone impls for all syntax tree