Reformat imports to a consistent style for imports

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

runtime/benches/bloom.rs

@@ -1,17 +1,18 @@
 #![feature(test)]
 
 extern crate test;
-use bv::BitVec;
-use fnv::FnvHasher;
-use rand::Rng;
-use solana_runtime::bloom::{AtomicBloom, Bloom, BloomHashIndex};
-use solana_sdk::{
-    hash::{hash, Hash},
-    signature::Signature,
+use {
+    bv::BitVec,
+    fnv::FnvHasher,
+    rand::Rng,
+    solana_runtime::bloom::{AtomicBloom, Bloom, BloomHashIndex},
+    solana_sdk::{
+        hash::{hash, Hash},
+        signature::Signature,
+    },
+    std::{collections::HashSet, hash::Hasher},
+    test::Bencher,
 };
-use std::collections::HashSet;
-use std::hash::Hasher;
-use test::Bencher;
 
 #[bench]
 #[ignore]