Change the description of xs.indices in the quickref

[Filip-afKlinteberg]

The current description of xs.indices in the quickref reads as follows: "Returns a Range extending from 0 to xs.length - 1".

During lectures and in the compendium (Assignment 7.2.3a) it's instead described as a Range from 0 until xs.length.

I think that it's better with a uniform description, so I suggest that the description in the quickref should be updated.