update pubmed url schema.

[mashehu]

Minor thing, because pubmed resolves the old url into the new ones on their end, but good to fix anyway.

PR checklist

• PR is to dev rather than master
• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated

[drpatelh]

Thanks! I used citedown.py to fetch and render the Markdown into something that is more malleable to insert into that document. This tool generates the URLs in the old format.

[drpatelh]

I guess it doesn't matter as much now because this process is still a manual one, and it works either way so I am not that fussed. Let's get your contribution into the codebase though!

[drpatelh]

LGTM! Fairly minor change where tests will be re-run on the PR from Dev -> Master again anyway. Thanks @mashehu !