doc: "moves" has a specific meaning in Rust, so avoid using it here

src/liballoc/boxed.rs

@@ -222,7 +222,7 @@ impl<T: ?Sized> Drop for IntermediateBox<T> {
 }
 
 impl<T> Box<T> {
-    /// Allocates memory on the heap and then moves `x` into it.
+    /// Allocates memory on the heap and then places `x` into it.
     ///
     /// # Examples
     ///