babel-preset-env: `DEBUG` option

Using targets:
{
  "chrome": "55",
  "uglify": true
}

Modules transform: false

Using plugins:
  check-es2015-constants {"uglify":true}
  transform-es2015-arrow-functions {"uglify":true}
  transform-es2015-block-scoped-functions {"uglify":true}
  transform-es2015-block-scoping {"uglify":true}
  transform-es2015-classes {"uglify":true}
  transform-es2015-computed-properties {"uglify":true}
  transform-es2015-destructuring {"uglify":true}
  transform-es2015-duplicate-keys {"uglify":true}
  transform-es2015-for-of {"uglify":true}
  transform-es2015-function-name {"uglify":true}
  transform-es2015-literals {"uglify":true}
  transform-es2015-object-super {"uglify":true}
  transform-es2015-parameters {"uglify":true}
  transform-es2015-shorthand-properties {"uglify":true}
  transform-es2015-spread {"uglify":true}
  transform-es2015-sticky-regex {"uglify":true}
  transform-es2015-template-literals {"uglify":true}
  transform-es2015-typeof-symbol {"uglify":true}
  transform-es2015-unicode-regex {"uglify":true}
  transform-regenerator {"uglify":true}
  transform-exponentiation-operator {"uglify":true}
  transform-async-to-generator {"uglify":true}
  syntax-trailing-function-commas {"chrome":"55","uglify":true}

Using polyfills:
  es7.string.pad-start {"chrome":"55"}
  es7.string.pad-end {"chrome":"55"}
  web.timers {"chrome":"55"}
  web.immediate {"chrome":"55"}
  web.dom.iterable {"chrome":"55"}
src/in.js -> lib/in.js