Update edx link for computer science course

[charlottetan]

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What does this PR do?

Improve Repo
Addresses #3878
The link already exists, but now redirects to a different link, so this PR updates the link

For resources

Description

Why is this valuable (or not)?

How do we know it's really free?

For book lists, is it a book? For course lists, is it a course? etc.

Checklist:

• Not a duplicate
• Included author(s) if appropriate
• Lists are in alphabetical order
• Needed indications added (PDF, access notes, under construction)