pass array of layers to `VREffect#requestPresent` (per spec change in MozVR/webvr-spec#28) (#8613)

examples/js/effects/VREffect.js

@@ -165,7 +165,7 @@ THREE.VREffect = function ( renderer, onError ) {
 
 				if ( boolean ) {
 
-					resolve( vrHMD.requestPresent( { source: canvas } ) );
+					resolve( vrHMD.requestPresent( [ { source: canvas } ] ) );
 
 				} else {