fix(modal): switch to .append
fix(modal): switch to .append

- Switch to `append` since `html` is jQuery specific

Closes #6187
Fixes #6186

looker/bootstrap,angular-ui/bootstrap,vfiles/bootstrap,fpipita/bootstrap,BookingBug/bootstrap,RobJacobs/bootstrap,shootermv/bootstrap,fpipita/bootstrap,vfiles/bootstrap,Servoy/bootstrap,icfantv/bootstrap,caoruiy/bootstrap,caoruiy/bootstrap,looker/bootstrap,angular-ui/bootstrap,RobJacobs/bootstrap,Kpler/bootstrap,icfantv/bootstrap,Kpler/bootstrap,shootermv/bootstrap,BookingBug/bootstrap,byronigoe/bootstrap,byronigoe/bootstrap,Servoy/bootstrap