fix: expdiff increases difficulty
fix: expdiff increases difficulty

pipermerriam/pyethereum,inzem77/pyethereum,shahankhatch/pyethereum,vaporry/pyethereum,karlfloersch/pyethereum,harlantwood/pyethereum,holiman/pyethereum,ethereum/pyethereum,ckeenan/pyethereum,shahankhatch/pyethereum,karlfloersch/pyethereum,pipermerriam/pyethereum,ethereum/pyethereum