Update Distributed Systems edition from 3rd to 4th

[double-tilde]

What does this PR do?

Changes the version of this book from the 3rd to 4th edition, making it more up to date.

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Description

Why is this valuable (or not)?

Keeps the resource up to date

How do we know it's really free?

It's from the same website as the 3rd edition, the 4th edition is also free and I have downloaded it myself today

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

Checklist:

• Search for duplicates.
• Include author(s) and platform where appropriate.
• Put lists in alphabetical order, correct spacing.
• Add needed indications (PDF, access notes, under construction).
• Used an informative name for this pull request.

Follow-up

• Check the status of GitHub Actions and resolve any reported warnings!

[eshellman]

Thanks, and welcome to free-programming-books!