avoid babel warnings
avoid babel warnings

douglasduteil/builder,whitneyit/builder,lookfirst/builder,jrauschenbusch/builder,systemjs/builder,alexisvincent/builder,jrauschenbusch/builder,lookfirst/builder,systemjs/builder,douglasduteil/builder,systemjs/builder,alexisvincent/builder,jrauschenbusch/builder,alexisvincent/builder,whitneyit/builder