Documentation: Lifecycle hooks example is wrong

[schontz]

Describe the bug

https://github.com/sveltejs/svelte/blob/main/documentation/docs/06-runtime/03-lifecycle-hooks.md

The theme change callback, toggle is incorrect. The linked "After" code is correct, though.

Reproduction

toggleValue is undefined

Logs

System Info

n/a

Severity

annoyance

[schontz]

svelte/documentation/docs/06-runtime/03-lifecycle-hooks.md

Lines 149 to 151 in 474c588

	function toggle() {
	toggleValue = !toggleValue;
	}