loader-merge: Fix usage of object-rest-spread

[AlanFoster]

According to the current version of babel, the usage of the object rest spread plugin name should be prefixed with transform

{
  "plugins": [
    ["transform-object-rest-spread", { "useBuiltIns": true }]
  ]
}

https://babeljs.io/docs/plugins/transform-object-rest-spread/#via-node-api

[edmorley]

Thank you for the PR! Keeping the docs up to date is really important.

The master branch is now using Babel 7, whose preset-env includes this plugin, which has also been renamed to proposal-object-rest-spread:
https://github.com/babel/babel/blob/v7.0.0-beta.47/packages/babel-preset-env/data/plugins.json#L227

Given that the plugin is now included, I wonder if there is another example "not-included-by-default" plugin we can use instead? Or else something generic like 'my-babel-plugin' so it never goes out of date causing confusion?

It would be good to fix the docs on the release/v8 branch to use the correct Babel 6 name of transform-object-rest-spread though.

[edmorley]

Also, the docs are in two places in the repo - once under docs/packages/ and once under packages/ (an unfortunate side-effect of our current hosting strategy; soon to be fixed). Could you update both locations? :-)

[eliperelman]

@AlanFoster would you be willing to update this PR based on @edmorley's comments?

[AlanFoster]

something generic like 'my-babel-plugin' so it never goes out of date causing confusion?

Good idea! PR updated 👍

[edmorley]

This looks great! Many thanks for the PR :-)

[edmorley]

The failed Netlify build is because master was broken at the time of the PR, so just going to ignore that result and merge anyway.

After this PR, I think we should also add object-rest-spread to the web preset on release/v8 as well as backport this docs fix there - which should help further with #883.