Replace nonexistent .col-6 classes in offcanvas example with .col-xs-6
Replace nonexistent .col-6 classes in offcanvas example with .col-xs-6

BS3 commits: ce7363e0dbdd2ebe03f58acb37fbe493ebcd1db5

todc/todc-bootstrap,aaroncnhk/todc-bootstrap,2947721120/googlebt4,todc/todc-bootstrap,todc/todc-bootstrap,up2vs/todc-bootstrap,ztx1491/todc-bootstrap,mozillo/todc-bootstrap,2947721120/todc-bootstrap