replace dead links

[jtbx]

Found with the following script

for link in $(grep -Eor 'https?://[^\\)", ]+' | grep -v dlang.org \
| grep -Eo 'https?://.+'); do (printf "%s: " "$link"; curl -Is "$link" \
| head -n1) | grep -E '4..$'; done

for link in $(grep -Eor '\\$\\(HTTP .+, ' | grep -v dlang.org \
| cut -d' ' -f2- | sed 's/, .*$//'); do out="$(curl -Is "$link")"; \
(! [ $? = 0 ] || printf '%s' "$out" | head -n1 | grep -Eq '4..') \
&& printf '%s\\n' "$link"; done

[dlang-bot]

Thanks for your pull request and interest in making D better, @jtbx! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + phobos#9023"