Reformat imports to a consistent style for imports

rustfmt.toml configuration:
  imports_granularity = "One"
  group_imports = "One"

frozen-abi/src/hash.rs

@@ -1,5 +1,7 @@
-use sha2::{Digest, Sha256};
-use std::{convert::TryFrom, fmt};
+use {
+    sha2::{Digest, Sha256},
+    std::{convert::TryFrom, fmt},
+};
 
 const HASH_BYTES: usize = 32;
 #[derive(AbiExample)]