webpack externals are still bundled in vue-cli

[rjm0017]

Version

3.0.0-rc.11

Node and OS info

node v8.11.3; npm v6.1.0; windows 10

Steps to reproduce

Reproduction steps in the readme of this repo: https://github.com/rjm0017/external-bundle-issue

What is expected?

vue-cli should be using the exports in vue.config.js to externalize three.js

What is actually happening?

bundle size is massive when three.js is imported, even with the externalization referenced from the vue-cli docs

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Reproduction can be done in https://github.com/rjm0017/external-bundle-issue and all of the steps are there

[yyx990803]

externals should be a package name, i.e. lowercase three, not THREE.