refactor(stats/incr/mrmse): fixed example/index.js

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---

Author: jsndz

lib/node_modules/@stdlib/stats/incr/nanmrmse/examples/index.js

@@ -41,5 +41,5 @@ for ( i = 0; i < 100; i++ ) {
 		v2 = ( randu()*100.0 ) - 50.0;
 	}
 	rmse = accumulator( v1, v2 );
-	console.log( '%d\t%d\t%d', v1.toFixed( 3 ), v2.toFixed( 3 ), rmse.toFixed( 3 ) );
+	console.log( '%d\t%d\t%d', v1.toFixed( 3 ), v2.toFixed( 3 ), ( rmse === null )? NaN : rmse.toFixed( 3 ) );
 }