docs/dev/build_the_docs: use direct links to requirements.txt

Created by: mkszuba

Use case

The links previously used here were, in spite of having .txt at the end, to respective GitHub HTML pages, which could come as a surprise to someone who saved the links directly from the ReadTheDocs page and then tried to feed the resulting files - with names still ending in .txt - to pip. Using direct links both is less confusing and saves one click each, regardless of whether one downloads the files or just passes links directly to 'pip -r'.

Description

Replaced old requirements.txt links in docs/dev/build_the_docs.rst to ones pointing directly to raw content.

Possible Drawbacks

None I can think of.

Testing

Have you added/modified unit tests to test the changes?

no

If so, do the tests pass/fail?

N/A

Have you run the entire test suite and no regression was detected?

I have rebuilt HTML documentation. Everything parses correctly and build_the_docs.html contains correct, updated links.