Fix variable name
Fix variable name

see also: https://github.com/ethereum/pyethereum/commit/611252b630981a93bd348cc3ed155a75ad71158b#commitcomment-18064088

shahankhatch/pyethereum,karlfloersch/pyethereum,karlfloersch/pyethereum,ethereum/pyethereum,shahankhatch/pyethereum,ethereum/pyethereum