bench: use string interpolation in stats/base/ndarray/dcovarmtk

PR-URL: #10875
Ref: #8647
Reviewed-by: Athan Reines <kgryte@gmail.com>

Author: Om-A-osc

lib/node_modules/@stdlib/stats/base/ndarray/dcovarmtk/benchmark/benchmark.js

@@ -22,6 +22,7 @@
 
 var bench = require( '@stdlib/bench' );
 var uniform = require( '@stdlib/random/array/uniform' );
+var format = require( '@stdlib/string/format' );
 var isnan = require( '@stdlib/math/base/assert/is-nan' );
 var pow = require( '@stdlib/math/base/special/pow' );
 var ndarray = require( '@stdlib/ndarray/base/ctor' );
@@ -114,7 +115,7 @@ function main() {
 	for ( i = min; i <= max; i++ ) {
 		len = pow( 10, i );
 		f = createBenchmark( len );
-		bench( pkg+':len='+len, f );
+		bench( format( '%s:len=%d', pkg, len ), f );
 	}
 }