add "setSize" method to WebGLRenderTarget

https://github.com/mrdoob/three.js/blob/master/src/renderers/WebGLRenderTarget.js#L40

threejs/three.d.ts

@@ -4517,6 +4517,7 @@ declare module THREE {
         generateMipmaps: boolean;
         shareDepthFrom: any;
 
+        setSize(width: number, height: number): void;
         clone(): WebGLRenderTarget;
         dispose(): void;