P3 preview branch build is failing

[web-padawan]

The same as vaadin/base-starter-vue#13

$ yarn build
yarn run v1.9.4
$ react-scripts build
Creating an optimized production build...
Failed to compile.

Failed to minify the code from this file:

 	./node_modules/@polymer/polymer/lib/utils/mixin.js:13

Need to find out what is the problem in UglifyJS, possibly create small reproduction.

[web-padawan]

See also https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/template/README.md#npm-run-build-fails-to-minify

even if a library provides an ES Modules version, it should still precompile other ES6 features to ES5 if it intends to support older browsers.

😐 really not sure how we could fix it ourselves, we could try to upgrade react-scripts to 2.0.0 preview release. At the moment of this writing, the latest published dev release is https://www.npmjs.com/package/react-scripts/v/2.0.0-next.a671462c

[web-padawan]

Note this is part of #12 but there are different problems there, too.

[web-padawan]

Fixed by #16 on the p3-preview branch, will merge to master once other starters are fixed.