fix minor bugs in export as (nbconvert) example
Update Export As (nbconvert).ipynb
widget_selection update

Fix for the fact that dictionary randomization sometimes switches the order of the arguments passed to the class on initialization.  This means that, potentially, 'value' can be updated BEFORE 'values', and since the method to update 'value' checks to see whether it exists in 'values', this breaks things.
Update widget_selection.py
Update widget_selection.py
Merge pull request #5493 from jdavidheiser/master

made a minor fix to one of the widget examples