Fix docs for Array#sort and Array#sort! [ci skip]

[repinel]

For better understanding, the block documentation should use x and y
(not a and b) to match the example given bellow.

[drbrain]

Can you make call-seq, text, and example all match?

Previously call-seq and text matched, with your current change text and example match.

[repinel]

@drbrain Sorry, it should all match now. Thanks for catching it.

[stomar]

Using |a, b| is very common for similar methods in various classes. So I think it would be definitely better (and simpler) to change x, y in the example to a, b.

(Personally, I don't think the example necessarily has to match the call-seq and text---in Ruby the block variables can be named arbitrarily of course---but it wouldn't hurt if they do.)

[stomar]

@repinel If you want to provide an updated commit I'll apply it.

[repinel]

@stomar What do you think of change?

[stomar]

Thanks for the update; the variables where switched, though, but I fixed it in the commit.

[repinel]

Thanks