Add sebastian serrano to CREDITS.
Add sebastian serrano to CREDITS.

tomholub/pycoin,Bluejudy/pycoin,XertroV/pycoin,thirdkey-solutions/pycoin,greenaddress/pycoin,mperklin/pycoin,richardkiss/pycoin,shivaenigma/pycoin,moocowmoo/pycoin,antiface/pycoin,lekanovic/pycoin,pycoin/pycoin,mperklin/pycoin,gitonio/pycoin,Bluejudy/pycoin,devrandom/pycoin,Kefkius/pycoin,Tetchain/pycoin,moocowmoo/pycoin,shivaenigma/pycoin,shayanb/pycoin,Treefunder/pycoin,pycoin/pycoin,Magicking/pycoin,ptcrypto/pycoin,shayanb/pycoin,richardkiss/pycoin,Treefunder/pycoin,thirdkey-solutions/pycoin,Kefkius/pycoin,tomholub/pycoin,zsulocal/pycoin,zsulocal/pycoin,lekanovic/pycoin,Magicking/pycoin,greenaddress/pycoin,Pan0ram1x/pycoin,gitonio/pycoin,Tetchain/pycoin,XertroV/pycoin,antiface/pycoin,ptcrypto/pycoin,Pan0ram1x/pycoin,devrandom/pycoin