* Add build script and remove babel
This change adds a build script which uses babel to transpile generated es6 source to es5, such that it can then be used in node projects or published as a package to npm. The `babel` package is also removed as it is deprecated, and superseded by `babel-cli`.
See https://github.com/OpenAPITools/openapi-generator/issues/2126#issuecomment-473926663
* update samples
