Update documentation for `SceneUtils.createMultiMaterialObject`

Change the return type to `THREE.Group` and clarify some of the grammar descripting the utility's function.

docs/api/extras/SceneUtils.html

@@ -16,14 +16,14 @@
 		<h2>Methods</h2>
 
 
-		<h3>[method:Object3D createMultiMaterialObject]( [page:Geometry geometry], [page:Array materials] )</h3>
+		<h3>[method:Group createMultiMaterialObject]( [page:Geometry geometry], [page:Array materials] )</h3>
 		<div>
-		geometry -- The geometry for the Object. <br />
+		geometry -- The geometry for the set of materials. <br />
 		materials -- The materials for the object.
 		</div>
 		<div>
-		Creates an new Object3D an new mesh for each material defined in materials. Beware that this is not the same as MultiMaterial which defines multiple material for 1 mesh.<br />
-		This is mostly useful for object that need a material and a wireframe implementation.
+		Creates a new Group that contains a new mesh for each material defined in materials. Beware that this is not the same as MultiMaterial which defines multiple material for 1 mesh.<br />
+		This is mostly useful for objects that need both a material and a wireframe implementation.
 		</div>
 
 		<h3>[method:null attach]( [page:Object3D child], [page:Object3D scene], [page:Object3D parent] )</h3>