Remove a class from an element
@param  {Element} element
@param  {Array.<string>|String} array of classnames or string with
@return {Element}
function removeClass(element, className) {
  var classNames = className;

  function _removeClass(el, cn) {
    var classRegex;
    if (el.classList) {
      el.classList.remove(cn);
    } else {
      classRegex = new RegExp('(?:^|\\s)' + cn + '(?!\\S)', 'g');
      el.className = el.className.replace(classRegex, '').trim();
    }
  }

  if (!isArray(className)) {
    classNames = className.trim().split(/\s+/);
  }
  classNames.forEach(_removeClass.bind(null, element));

  return element;
}