Webpack: Fix reference to past lesson

[MaoShizhong]

Because

One paragraph mistakenly says a topic was covered in the previous lesson but it's actually covered in the lesson before that (was originally written before the decision was made to split off the npm topic to a new lesson).

This PR

• Fixes past lesson reference for a topic.

Issue

Closes #XXXXX

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide

[KevinMulhern]

Thanks @MaoShizhong!