Don't use es2015 preset for babel

[tracker1]

You should use the env preset, and configure it for the node and chrome versions matching your electron dist... most of the es2015 transforms are not needed in the latest versions... This will reduce your JS output by at least 1/3 and probably closer to half.

[Fohlen]

@tracker1 thanks for noting! Maybe you would like to make this a good first issue and submit a PR for it 🥂