fix: Replace "last" with "first"

[abdoemadselim]

Clicking on "Remove first thing" button removes the first component not the last

How to produce:

1. Go to https://svelte.dev/tutorial/svelte/keyed-each-blocks
2. See the lesson description on the left
3. See the

Click the 'Remove first thing' button a few times, and notice what happens:

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[7nik]

The first item of the array is removed, and it is so visually in the solved lesson.