add domElement
add domElement

To match the documentation: https://threejs.org/docs/#examples/en/controls/TransformControls
TransformControls should expose a `domElement` property.

````
.domElement : HTMLDOMElement
The HTMLDOMElement used to listen for mouse / touch events. This must be passed in the constructor; changing it here will not set up new event listeners.
````
greggman/three.js,looeee/three.js,Samsy/three.js,fraguada/three.js,kaisalmen/three.js,stanford-gfx/three.js,jpweeks/three.js,fyoudine/three.js,TristanVALCKE/three.js,zhoushijie163/three.js,Itee/three.js,TristanVALCKE/three.js,gero3/three.js,Samsy/three.js,fraguada/three.js,Samsy/three.js,looeee/three.js,TristanVALCKE/three.js,donmccurdy/three.js,jpweeks/three.js,06wj/three.js,fyoudine/three.js,Samsy/three.js,TristanVALCKE/three.js,Samsy/three.js,kaisalmen/three.js,mrdoob/three.js,fraguada/three.js,makc/three.js.fork,stanford-gfx/three.js,WestLangley/three.js,gero3/three.js,greggman/three.js,mrdoob/three.js,WestLangley/three.js,donmccurdy/three.js,Liuer/three.js,TristanVALCKE/three.js,makc/three.js.fork,aardgoose/three.js,Samsy/three.js,fraguada/three.js,fraguada/three.js,TristanVALCKE/three.js,Itee/three.js,06wj/three.js,zhoushijie163/three.js,Liuer/three.js,aardgoose/three.js,fraguada/three.js