Test project for a bug using rollup with D3 micro-libraries.
$ npm install
$ npm run build
That will install the dependencies and build the simple JavaScript file.
If you grep the generated main.js for defaultLocale you'll find that it is
called, but the function definition is not included.
You can also start up a webserver and load index.html in a browser. In the
console you'll see a ReferenceError stating that defaultLocale is not defined. It is visible in the sourcemap, but it isn't present in the
generated file.