the basefee opcode (#142)

Signed-off-by: xermicus <cyrill@parity.io>

crates/integration/src/tests.rs

@@ -49,6 +49,7 @@ test_spec!(delegate, "Delegate", "Delegate.sol");
 test_spec!(gas_price, "GasPrice", "GasPrice.sol");
 test_spec!(gas_left, "GasLeft", "GasLeft.sol");
 test_spec!(gas_limit, "GasLimit", "GasLimit.sol");
+test_spec!(base_fee, "BaseFee", "BaseFee.sol");
 
 fn instantiate(path: &str, contract: &str) -> Vec<SpecsAction> {
     vec![Instantiate {