Reformat use declarations.

The previous commit updated `rustfmt.toml` appropriately. This commit is
the outcome of running `x fmt --all` with the new formatting options.

compiler/rustc_data_structures/src/packed.rs

@@ -1,8 +1,10 @@
-use crate::stable_hasher::{HashStable, StableHasher};
-use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use std::cmp::Ordering;
 use std::fmt;
 
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
+
+use crate::stable_hasher::{HashStable, StableHasher};
+
 /// A packed 128-bit integer. Useful for reducing the size of structures in
 /// some cases.
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]