Notebook 7 link to other fastai notebook results in a 404 error

[magic-lantern]

Currently reviewing notebook 7 (https://github.com/fastai/course-nlp/blob/master/7-seq2seq-translation.ipynb) and there are a few places that links to another fastai notebook.

At the beginning of notebook 7 it says:

This notebook is modified from [this one](https://github.com/fastai/fastai_docs/blob/master/dev_course/dl2/translation.ipynb) created by Sylvain Gugger.

And later:

[fast.ai implementation of seq2seq with QRNNs](https://github.com/fastai/fastai_docs/blob/master/dev_course/dl2/translation.ipynb)

I see the fastai_docs repo is now actually fastai_dev which is rapidly changing right now. Perhaps this is the notebook that should be referenced?

https://github.com/fastai/fastai_dev/blob/master/dev_nb/translation_pretrained.ipynb

[magic-lantern]

Just found this other version in the current Fast.Ai course repo:

https://github.com/fastai/course-v3/blob/master/nbs/dl2/translation.ipynb

And this related one:

https://github.com/fastai/course-v3/blob/master/nbs/dl2/translation_transformer.ipynb

I'm happy to do a pull request, just want someone who know best to say which link it should use.