Refactored swap_remove doc comment upon discussing with BurntSushi and steveklabnik

Author: mandeep

src/libcollections/vec.rs

@@ -678,8 +678,9 @@ impl<T> Vec<T> {
         self.len = len;
     }
 
-    /// Removes an element from anywhere in the vector and returns it, replacing
-    /// it with the last element.
+    /// Removes an element from the vector and returns it.
+    /// 
+    /// The removed element is replaced by the last element of the vector.
     ///
     /// This does not preserve ordering, but is O(1).
     ///