Update lesson.md

[esma-g]

What does this change?

Module: Node Week(s): 4

Checklist

• [x] I have read the contributing guidelines
• [x] I have checked my spelling and grammar with an automated tool
• [x] I have previewed my changes to check the markdown renders as I intend
• [x] I have run my code to check it works
• [x] My changes follow our Style Guide

Description

Minor edit, week 4 title used to say week 3

Who needs to know about this?

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