Update pycoin version to 0.51
Update pycoin version to 0.51

stefcrypto/counterparty-lib,Reddcraft/reddcraftd,CounterpartyXCP/counterparty-lib,Reddcraft/reddcraftd,monaparty/counterparty-lib,Paytokens/paytokensd,Ziftr/counterpartyd,Litetokens/litetokensd,CounterpartyXCP/counterparty-lib,tokenly/counterparty-lib,Ziftr/counterpartyd,F483/counterparty-lib,F483/counterparty-lib,Tetchain/tetchaind,monaparty/counterparty-lib,gotcha/testcounter,ClearingHouse/clearinghoused,coinwarp/dogeparty-lib,ClearingHouse/clearinghoused,Bluejudy/bluejudyd,Tetchain/tetchaind,Bluejudy/bluejudyd,jarymoth/counterpartyd