Patch neg sampling

[armingh2000]

Description of changes:
For negative sampling, the get_negatives function is not working properly. I changed the way it iterates through the dictionary. It works fine now.

@AnirudhDagar I made 2 commits here. The first is for .md file. The second one is after running d2lbook build lib and nothing else was changed thereafter. But there are no imports in torch.py file :|

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[AnirudhDagar]

This has been opened in favour of #1793.
No worries @armingh2000! Thanks for your contributions, I've made the change for rest of it.

[AnirudhDagar]

LGTM! Will wait for @astonzhang to merge and double check this.

[armingh2000]

@AnirudhDagar Thanks a lot for your patience. Can you say where did I get wrong? Just for further contributions, I am asking.

[mli]

Job d2l-en/PR-1796/2 is complete.
Check the results at http://preview.d2l.ai/d2l-en/PR-1796/

[AnirudhDagar]

@armingh2000 I'm not very sure why the d2lbook build lib command missed imports on your machine. Please make sure that the chapter preface was there in your local repo, since all the imports reside there.

If that doesn't solve the problem, i think it might be a windows only issue, you can go ahead and raise an issue on the d2lbook github repo for that.

[armingh2000]

@AnirudhDagar yes I think you're right. I'll check that out. Thanks

[astonzhang]

@armingh2000 Great catch! I'll further simplify your proposed change as
sampling_weights = [count**0.75 for count in counter.values()]

[astonzhang]

@armingh2000, would you like to send another PR to replace your id with name in our acknowledgement:
https://github.com/d2l-ai/d2l-en/blob/master/chapter_preface/index.md

Thanks!

[armingh2000]

@astonzhang yes that would be better. Should I change the related .md file and compile after that? If not, how can I change my id to my name?
Thanks

[astonzhang]

@astonzhang yes that would be better. Should I change the related .md file and compile after that? If not, how can I change my id to my name?
Thanks

You may wish to refer to 19.6.1 https://d2l.ai/chapter_appendix-tools-for-deep-learning/contributing.html on how to edit the md file (replacing id with name)