tour: Possible Typo

[benlevycmp]

Context: https://go.dev/tour/moretypes/10

Where it says "The default is zero for the low bound and the length of the slice for the high bound," it seems like the high bound should be the length of the array rather than the length of the slice.

As I understand it, the slice doesn't have a length until it is made, so it doesn't make sense to reference it in it's own creation.