fix for safari webworkers https://bugs.webkit.org/show_bug.cgi?id=119472
fix for safari webworkers https://bugs.webkit.org/show_bug.cgi?id=119472

alexisvincent/builder,systemjs/builder,alexisvincent/builder,systemjs/builder,jrauschenbusch/builder,jrauschenbusch/builder,systemjs/builder,alexisvincent/builder,jrauschenbusch/builder