Fixes#4691Fixes#4614
This PR gives path to https://github.com/zeit/next-plugins/pull/242
I did not add or remove `^` near dependency versions in package.json files. However, I don't exclude that some changes can be made given that rc is more stable than beta.
## Issue
Running [examples/with-custom-babel-config](https://github.com/zeit/next.js/tree/canary/examples/with-custom-babel-config) will result in the following error message:
```
./pages/index.js
Module build failed (from /some_path/next.js/dist/build/webpack/loaders/next-babel-loader.js):
Error: [BABEL] /some_path/next.js/examples/with-custom-babel-config/pages/index.js:
As of v7.0.0-beta.55, we've removed Babel's Stage presets.
Please consider reading our blog post on this decision at
https://babeljs.io/blog/2018/07/27/removing-babels-stage-presets
for more details. TL;DR is that it's more beneficial in the
long run to explicitly add which proposals to use.
...
```
## Explanation
Babel removed Babel's Stage presets on July 27, 2018.
More info: https://babeljs.io/blog/2018/07/27/removing-babels-stage-presets
## Solution
I've updated the example so ist just uses the babel plugin it actually needs.
## Related
Closes: #4772
The option `"decoratorsLegacy": true` seems mandatory, fails without it:
> The new decorators proposal is not supported yet. You must pass the `"decoratorsLegacy": true` option to @babel/preset-stage-0
