WebGLAttributes: Remove overlooked var.

src/renderers/webgl/WebGLAttributes.js

@@ -140,7 +140,7 @@ function WebGLAttributes( gl, capabilities ) {
 
 		if ( attribute.isGLBufferAttribute ) {
 
-			var cached = buffers.get( attribute );
+			const cached = buffers.get( attribute );
 
 			if ( ! cached || cached.version < attribute.version ) {