Fix missing imports in tests I had missed

ethcore/src/json_tests/test_common.rs

@@ -14,6 +14,8 @@
 // You should have received a copy of the GNU General Public License
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
+pub use bigint::prelude::U256;
+pub use bigint::hash::H256;
 pub use util::*;
 use std::collections::HashSet;
 use std::io::Read;

ethcore/src/json_tests/trie.rs

@@ -16,7 +16,7 @@
 
 use ethjson;
 use util::trie::{TrieFactory, TrieSpec};
-use util::hash::H256;
+use bigint::hash::H256;
 use util::memorydb::MemoryDB;
 
 fn test_trie(json: &[u8], trie: TrieSpec) -> Vec<String> {