Consider to use babel-plugin-transform-helper as lighter alternative to transform-runtime

[narqo]

It feels that transform-runtime is huge.

As we don't use any particular things of runtime / core-js, babel-plugin-external-helpers could be a better choice.

See

• http://www.2ality.com/2015/12/babel6-helpersstandard-library.html
• http://bran.name/articles/babel-transforms-helpers-polyfills/