Fix der.py for Python 3.
Fix der.py for Python 3.

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