Update decoder.py
Update decoder.py

pylint
ufal/neuralmonkey,juliakreutzer/bandit-neuralmonkey,ufal/neuralmonkey,juliakreutzer/bandit-neuralmonkey,ufal/neuralmonkey,ufal/neuralmonkey,juliakreutzer/bandit-neuralmonkey,juliakreutzer/bandit-neuralmonkey,ufal/neuralmonkey,juliakreutzer/bandit-neuralmonkey