Add samples to WebGLMultisampleRenderTarget.d.ts.

src/renderers/WebGLMultisampleRenderTarget.d.ts

@@ -13,4 +13,9 @@ export class WebGLMultisampleRenderTarget extends WebGLRenderTarget {
 
 	readonly isWebGLMultisampleRenderTarget: true;
 
+	/**
+	 * Specifies the number of samples to be used for the renderbuffer storage.However, the maximum supported size for multisampling is platform dependent and defined via gl.MAX_SAMPLES.
+	 */
+	samples: number;
+
 }