code: function ancestors(first, second) {
    var path = [];
  
    for (var n in first.path) {
      if (first.path[n] !== second.path[n]) break;
      path.push(first.path[n]);
    }
    return path;
  }
docs: Finds the common ancestor path between two states.
  
  @param {Object} first The first state.
  @param {Object} second The second state.
  @return {Array} Returns an array of state names in descending order, not including the root.