bench: explicitly specify separator dtype

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

Author: kgryte

lib/node_modules/@stdlib/blas/ext/base/ndarray/gjoin/benchmark/benchmark.js

@@ -54,7 +54,9 @@ function createBenchmark( len ) {
 	xbuf = uniform( len, 0.0, 100.0, options );
 	x = new ndarray( options.dtype, xbuf, [ len ], [ 1 ], 0, 'row-major' );
 
-	separator = scalar2ndarray( ',', options );
+	separator = scalar2ndarray( ',', {
+		'dtype': 'generic'
+	});
 
 	return benchmark;