fix: highlight code diff for invoice.jsx

[jimniels]

The very last example in the tutorial is highlighting the wrong lines of code.

The last time this file was touched in the tutorial, it looked like this:

Then, when you get to the next place invoices.jsx is edited, the diff highlights are incorrect. Note:

• 👍 The import diffs is right
• 👎 Lines 9 and 10 (useNavigate() and useLocation()) were added but not highlighted as additions
• 👎 Lines 20-29 are highlighted, but line 20 was already there and line 30 was added (but not highlighted).

So this request makes it so the actual code differences are highlighted correctly. Current vs. proposed:

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[remix-cla-bot]

Thank you for signing the Contributor License Agreement. Let's get this merged! 🥳