Update set.rs

Author: frehberg

src/libstd/collections/hash/set.rs

@@ -100,7 +100,7 @@ const INITIAL_CAPACITY: usize = 32;
 ///     println!("{:?}", x);
 /// }
 /// ```
-/// HashSet with fixed list of elements can be initialized from vector:
+/// HashSet with fixed list of elements can be initialized from an array:
 /// ```
 /// use std::collections::HashSet;
 ///