`Benchmark` may not be browser global in ESM bundle

[loynoir]

Scenario

Using rollup generate ESM bundle for browser

Expected

ESM bundle works with no Benchmark in browser global

Actual

Browser all failed error, complains there is no global Benchmark.

Related line

benchmark.js/benchmark.js

Line 666 in 42f3b73

prefix = '(' + (freeDefine ? 'define.amd.' : 'Benchmark.') + prop + '||function(){})();';

Should fixed in pull

#245