remove six dependency
remove six dependency

harlantwood/pyethereum,shahankhatch/pyethereum,karlfloersch/pyethereum,jnnk/pyethereum,karlfloersch/pyethereum,inzem77/pyethereum,vaporry/pyethereum,shahankhatch/pyethereum,ethermarket/pyethereum,pipermerriam/pyethereum,ddworken/pyethereum,ethers/pyethereum,ckeenan/pyethereum,holiman/pyethereum,ethereum/pyethereum,ethereum/pyethereum,pipermerriam/pyethereum