Problem in advanced NLP tutorial

[fsonntag]

@ZhixiuYe pointed out a problem in the Viterbi Decoder in the original repository:
rguthrie3/DeepLearningForNLPInPytorch#8

Him and me proposed some possible fixes. What do you guys think about that?

[chsasank]

Hey @fsonntag, I see that original issue was fixed. It'd be nice if you can push that fix here too.