order derivable traits lists

Ignoring :
 - **generated**.rs
 - python/tidy/servo_tidy_tests/rust_tidy.rs

components/script/dom/bindings/iterable.rs

@@ -22,7 +22,7 @@ use std::cell::Cell;
 use std::ptr;
 
 /// The values that an iterator will iterate over.
-#[derive(JSTraceable, HeapSizeOf)]
+#[derive(HeapSizeOf, JSTraceable)]
 pub enum IteratorType {
     /// The keys of the iterable object.
     Keys,