Fix spelling of "Known problems section" of interior_mutable_key

Author: flip1995

clippy_lints/src/mut_key.rs

@@ -12,10 +12,10 @@ declare_clippy_lint! {
     /// `BtreeSet` rely on either the hash or the order of keys be unchanging,
     /// so having types with interior mutability is a bad idea.
     ///
-    /// **Known problems:** It's correct to use a struct, that contains interior mutability,
-    /// as a key; when its `Hash` implementation doesn't access any these interior mutable types.
-    /// However, this lint is unable to recognise it so cause a false positive.
-    /// `bytes` ctate is a great example of this.
+    /// **Known problems:** It's correct to use a struct, that contains interior mutability
+    /// as a key, when its `Hash` implementation doesn't access any of the interior mutable types.
+    /// However, this lint is unable to recognize this, so it causes a false positive in theses cases.
+    /// The `bytes` crate is a great example of this.
     ///
     /// **Example:**
     /// ```rust