tour: inaccuracy on "Slice defaults" page

[jacobshandling]

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

Description currently reads:

When slicing, you may omit the high or low bounds to use their defaults instead.

The default is zero for the low bound and the length of the slice for the high bound.

This should say something like "..and the length of the operand (array or slice) for the high bound."

[crisman]

Fixed in https://github.com/golang/website/pull/209, which is not yet merged.