function getOppositePlacement(placement) {
  var hash = { left: 'right', right: 'left', bottom: 'top', top: 'bottom' }
  return placement.replace(/left|right|bottom|top/g, function (matched) {
    return hash[matched]
  })
}
Get the opposite placement of the given one/
@function
@ignore
@argument {String} placement
@returns {String} flipped placement