docs: new WebGLRenderTarget has optional parameters

https://github.com/mrdoob/three.js/blob/9ee6ec8fcf6ef04a4fc53d9e58070093899790c3/examples/webgl2_rendertarget_texture2darray.html#L134
 is an example of this.

docs/api/en/renderers/WebGLRenderTarget.html

@@ -23,8 +23,8 @@
 		<h3>[name]([param:Number width], [param:Number height], [param:Object options])</h3>
 
 		<p>
-		[page:Float width] - The width of the renderTarget. <br />
-		[page:Float height] - The height of the renderTarget.<br />
+		[page:Float width] - (optional) The width of the renderTarget.<br />
+		[page:Float height] - (optional) The height of the renderTarget.<br />
 		options - (optional object that holds texture parameters for an auto-generated target
 		texture and depthBuffer/stencilBuffer booleans.