New: Drop supports for Node.js 8.x and 11.x (#44)

designs/2019-drop-node8/README.md

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+- Start Date: 2019-10-13
+- RFC PR: https://github.com/eslint/rfcs/pull/44
+- Authors: Toru Nagashima ([@mysticatea](https://github.com/mysticatea))
+
+# Drop supports for Node.js 8.x and 11.x
+
+## Summary
+
+This RFC drops supports for Node.js 8.x and 11.x because of end-of-life. (See [nodejs/release](https://github.com/nodejs/release#readme) to check the release schedule of Node.js)
+
+## Motivation
+
+We get the capability to use new features and syntaxes by dropping the support for end-of-life versions of Node.js. Especially, [RFC40](https://github.com/eslint/rfcs/pull/40) wants to use async iteration, but Node.js 8.x doesn't support that syntax.
+
+## Detailed Design
+
+This proposal updates the `engines` field of our `package.json` (and updates our CI scripts).
+
+```diff
+   "engines": {
+-    "node": "^8.10.0 || ^10.13.0 || >=11.10.1"
++    "node": "^10.12.0 || >=12.0.0"
+   }
+```
+
+### Why is it `^10.12.0`?
+
+> **Resolution:** We will choose Node version support based on the lowest point release supporting our desired features.
+>
+> [2019-March-14 ESLint TSC Meeting Notes: Decide how to manage support for minor versions of Node](https://github.com/eslint/tsc-meetings/blob/137fbe2be55499cd75f28a008900803078d22dfd/notes/2019/2019-03-14.md#decide-how-to-manage-support-for-minor-versions-of-node)
+
+Therefore, we should check the added features in Node.js `10.x`.
+
+I found two features we want to use.
+
+- [10.10.0](https://nodejs.org/en/blog/release/v10.10.0/) ... the `withFileTypes` option of `fs.readdir`/`fs.readdirSync`. We can reduce the calls of `fs.statSync` in our `FileEnumerator` class with this option. It may improve performance (especially on Windows).
+- [10.12.0](https://nodejs.org/en/blog/release/v10.12.0/) ... `module.createRequireFromPath(filename)` function. We can remove [our polyfill](https://github.com/eslint/eslint/blob/24ca088fdc901feef8f10b050414fbde64b55c7d/lib/shared/relative-module-resolver.js#L20-L29) with this version.
+
+## Documentation
+
+We need write an entry in the migration guide because this is a breaking change.
+
+## Drawbacks
+
+Users lose the capability to run ESLint on old Node.js. They may have to update their CI scripts.
+
+## Backwards Compatibility Analysis
+
+This is a breaking change clearly.
+
+Users lose the capability to run ESLint on old Node.js. They may have to update their CI scripts.
+
+## Alternatives
+
+N/A.
+
+## Related Discussions
+
+- https://github.com/eslint/eslint/issues/10981 - Allow use node version >8
+- https://github.com/eslint/eslint/issues/11022 - Decide how to manage support for minor versions of Node