Mandated upgrade: Node.js 8.x LTS Carbon is no longer actively supported

**Description**

As part of docker build I got this deprecation message:
```
DEPRECATION WARNING

Node.js 8.x LTS Carbon is no longer actively supported!

You will not receive security or critical stability updates for this version.

You should migrate to a supported version of Node.js as soon as possible.
Use the installation script that corresponds to the version of Node.js you
wish to install. e.g.

* https://deb.nodesource.com/setup_10.x — Node.js 10 LTS "Dubnium" (recommended)
* https://deb.nodesource.com/setup_12.x — Node.js 12 LTS "Erbium"

Please see https://github.com/nodejs/Release for details about which
version may be appropriate for you.

The NodeSource Node.js distributions repository contains
information both about supported versions of Node.js and supported Linux
distributions. To learn more about usage, see the repository:
https://github.com/nodesource/distributions
```

Looks like a bunch of busy work is required to stay in place. Any idea how terrible an ordeal this will be?

Docker のビルド設定から始めて、Node.js 8.x がインストールされている場所を特定してください。Issue にリンクされているサポート対象の Node.js インストールガイダンスを確認し、関連するビルド設定を更新して、Docker ビルドで非推奨警告が出力されなくなったことを確認してください。

索引モデルが issue の本文から書いたものです。