fix(dom): EventDelegator shouldnt register duplicate event listeners
fix(dom): EventDelegator shouldnt register duplicate event listeners

The correct data structure for domListenersToAdd should be a "Set" (we
used Map, though), not an array.

cyclejs/cyclejs,cyclejs/cyclejs,ntilwalli/cyclejs,ntilwalli/cyclejs,staltz/cycle,cyclejs/cycle-core,cyclejs/cyclejs,cyclejs/cycle-core,cyclejs/cyclejs,ntilwalli/cyclejs,staltz/cycle,ntilwalli/cyclejs