Link fix

Author: alex-semenyuk

clippy_lints/src/await_holding_invalid.rs

@@ -15,7 +15,7 @@ declare_clippy_lint! {
     /// `MutexGuard`.
     ///
     /// ### Why is this bad?
-    /// The Mutex types found in [`std::sync`][https://doc.rust-lang.org/stable/std/sync/] and
+    /// The Mutex types found in [`std::sync`](https://doc.rust-lang.org/stable/std/sync/) and
     /// [`parking_lot`](https://docs.rs/parking_lot/latest/parking_lot/) are
     /// not designed to operate in an async context across await points.
     ///