Why does examples/seq2seq/finetune.py only use sortish sampler for train? 
Would it make eval faster?
Would it make validation sanity check obnoxiously slow?
This should be a ~1 line PR with a longer PR description.


@sshleifer I can help out here. What exactly are you looking for?<|||||>I'll take care of it actually, sorry! There is a harder one at #6785 if you're interested.<|||||>Fixed, using sortish sampler for val. Much faster!