bench: use correct specifier

Signed-off-by: Athan <kgryte@gmail.com>

Author: kgryte

lib/node_modules/@stdlib/array/base/filled/benchmark/benchmark.length.js

@@ -88,7 +88,7 @@ function main() {
 		len = pow( 10, i );
 
 		f = createBenchmark( len );
-		bench( format( '%s:len=%s', pkg, len ), f );
+		bench( format( '%s:len=%d', pkg, len ), f );
 	}
 }