Fix collection entry API documentation.

library/std/src/collections/mod.rs

@@ -268,7 +268,7 @@
 //! not. Normally, this would require a `find` followed by an `insert`,
 //! effectively duplicating the search effort on each insertion.
 //!
-//! When a user calls `map.entry(&key)`, the map will search for the key and
+//! When a user calls `map.entry(key)`, the map will search for the key and
 //! then yield a variant of the `Entry` enum.
 //!
 //! If a `Vacant(entry)` is yielded, then the key *was not* found. In this case