Fix #9521 - Single button in expanded button group
Fix #9521 - Single button in expanded button group

Fix https://github.com/zurb/foundation-sites/issues/9521
A single button in a expanded button group was not expanded.

Changes:
- Add `width:100%` to the button when it is the only one in the button
group.

Note: The way we are currently handling button groups is really dirty.

abdullahsalem/foundation-sites,abdullahsalem/foundation-sites,aoimedia/foundation,atmmarketing/foundation-sites,ucla/foundation-sites,denisahac/foundation-sites,zurb/foundation,ucla/foundation-sites,zurb/foundation-sites,brettsmason/foundation-sites,Owlbertz/foundation,colin-marshall/foundation-sites,zurb/foundation-sites,brettsmason/foundation-sites,denisahac/foundation-sites,Owlbertz/foundation,jamesstoneco/foundation-sites,dragthor/foundation-sites,ucla/foundation-sites,jamesstoneco/foundation-sites,zurb/foundation-sites,natewiebe13/foundation-sites,IamManchanda/foundation-sites,jeromelebleu/foundation-sites,aoimedia/foundation,zurb/foundation,denisahac/foundation-sites,jaylensoeur/foundation-sites-6,Owlbertz/foundation,brettsmason/foundation-sites,jaylensoeur/foundation-sites-6,IamManchanda/foundation-sites,aoimedia/foundation,jeromelebleu/foundation-sites,samuelmc/foundation-sites,zurb/foundation,Owlbertz/foundation,BerndtGroup/TBG-foundation-sites,samuelmc/foundation-sites,BerndtGroup/TBG-foundation-sites,BerndtGroup/TBG-foundation-sites,dragthor/foundation-sites,jaylensoeur/foundation-sites-6,atmmarketing/foundation-sites,natewiebe13/foundation-sites,dragthor/foundation-sites,DaSchTour/foundation-sites,jamesstoneco/foundation-sites,jeromelebleu/foundation-sites,colin-marshall/foundation-sites,natewiebe13/foundation-sites,DaSchTour/foundation-sites,IamManchanda/foundation-sites,samuelmc/foundation-sites,abdullahsalem/foundation-sites,atmmarketing/foundation-sites,colin-marshall/foundation-sites