separate semantic_version from util (#6438)

ethcore/src/ethereum/ethash.rs

@@ -35,6 +35,7 @@ use evm::Schedule;
 use ethjson;
 use rlp::{self, UntrustedRlp};
 use vm::LastHashes;
+use semantic_version::SemanticVersion;
 
 /// Parity tries to round block.gas_limit to multiple of this constant
 pub const PARITY_GAS_LIMIT_DETERMINANT: U256 = U256([37, 0, 0, 0]);