Select : prompt is no longer displayed

[tbergerd]

This is a regression at head I noticed.
cargo run --example select

Behavior :
The four options get displayed without the prompt
Expected :
the "Pick your flavor" prompt is correctly displayed (works fine in dialoguer 0.10.4)

Specifically the reg was introduced by fix #267
I'm under the impression Paging::update is only meant to be called after Paging::render_prompt
calling it before makes it so self.activity_transition is set to false (iff there is only one page. notice we do see the prompt correctly on the third part of the 'select' example because it has 2 pages)
here I think we only want to update self.current_page (to fix the issue mentioned in #267)

I'll try and submit a fix but I'm opening the issue in case what I propose is not what we want

[pksunkara]

I think that sounds about right.