added missing toJSON method (#10020)

docs/api/scenes/Scene.html

@@ -46,6 +46,11 @@
 
 		<h2>Methods</h2>
 
+		<h3>[method:JSON toJSON]</h3>
+		<div>
+		Return the scene data in JSON format.
+		</div>
+
 		<h2>Source</h2>
 
 		[link:https://github.com/mrdoob/three.js/blob/master/src/[path].js src/[path].js]