Make dropdown respect boundaries of browser

See it in action here: http://www.tangerineindustries.com/download/Foundation_Dropdown/index.html
Update foundation.dropdown.js

file failed with travis, resubmit
Update foundation.dropdown.js

travis failed, resubmitting, had undefined var.
Update foundation.dropdown.js
Update foundation.dropdown.js

Changes to fix medium grid break-point
Merge pull request #5986 from coreysyms/master

Fix: Make dropdown respect boundaries of browser Foundation 5