Fix tabs order, avoid appearance of tab header on next row

Avoid appearance of tab header on next row by rechecking offsets.
After pushing tabs, one of the pushed tabs may have `.active` class with bold font and that may result in undesirable push of the last visible tab header down to next row by the `li.tabdrop.active`
Update bootstrap-tabdrop.js
Fix for Bootstrap 3.3
Merge pull request #7 from pribilinskiy/patch-2

Fix tabs order, avoid appearance of tab header on next row