allow babel webpack configs

[deecewan]

Webpack provides the ability to append '.babel.js' instead of '.js', and the config will be parsed by babel before webpack uses it.

Webpack supports this using interpret and it's mentioned in webpack/webpack#1403

I currently use it for all my configs, so special is not picking them up

[codecov-io]

Current coverage is 98.14% (diff: 100%)

Merging #199 into master will not change coverage

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[lijunle]

The changes look good! Thank you!