dropdown: corrected a bug with classes in dropdown
dropdown: corrected a bug with classes in dropdown

wffranco/vue-strap,yuche/vue-strap,BiodataMiningGroup/vue-strap,wffranco/vue-strap,yuche/vue-strap,tonypee/vue-strap,lotestudio/vue-strap,BiodataMiningGroup/vue-strap,tonypee/vue-strap,lotestudio/vue-strap