Fix links to GitHub docs

[hwine]

Apparently, GitHub docs were changed to assume a default doc version of 'free-pro-team@latest', and droped support for specifying that explicitly.

Additionally, remove the '/en' locale specifier, so the browser can negotiate the appropriate one for every user.

Changes were done mechanically using

for f in $(rg '@latest' -l) ; do
    sed --in-place=.doc \
        -e 's:docs.github.com/en/free-pro-team@latest/:docs.github.com/:g' \
        $f
done

N.B. the CONTRIBUTING.md section on documentation changes appears to reference an older procedure. Please let me know if a different procedure should be used now.

Fixes #135

[review-notebook-app[bot]]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

---

Powered by ReviewNB

[jph00]

Many thanks!