Update doctest to [email protected]

[schillic]

This fixes the recent failure of the documentation build. It was caused by a new Symbolics release (v5.31.0), which changes the order of arguments.

Actually, I am not sure we should just change the doctest. I think this is a bad change in Symbolics:
Hyperplane(x - y == 2) should not translate to Hyperplane{Float64, Vector{Float64}}([-1.0, 1.0], 2.0).
I see two options:

1. Check whether we can change the translation in LazySets.
2. Restrict the Symbolics version to pre-v5.31.0.

EDIT: I asked in Symbolics#1182. They will add an argument for sorting to the function get_variables.