Fix typo in bs_collapse
Fix typo in bs_collapse

Thanks to NiklasTeich who reported the issue here: https://wordpress.org/support/topic/collapsibles-broken-after-six-collapse-items?replies=5
MWDelaney/bootstrap-3-shortcodes,MWDelaney/bootstrap-3-shortcodes,MWDelaney/bootstrap-3-shortcodes,filipstefansson/bootstrap-3-shortcodes,filipstefansson/bootstrap-3-shortcodes