src/lib/gesture.js
function getCommonAncestor(el1, el2) {
  var el = el1
  while (el) {
    if (el.contains(el2) || el == el2) {
      return el
    }
    el = el.parentNode
  }
  return null
}
function getCommonAncestor(el1, el2) {
  var el = el1
  while (el) {
    if (el.contains(el2) || el == el2) {
      return el
    }
    el = el.parentNode
  }
  return null
}
function getCommonAncestor ( el1 , el2 ) { var el = el1 while ( el ) { if ( el . contains ( el2 ) || el == el2 ) { return el } el = el . parentNode } return null }
find the closest common ancestor
if there's no one, return null

@param  {Element} el1 first element
@param  {Element} el2 second element
@return {Element}     common ancestor
find the closest common ancestor if there s no one return null