message: recommend eslint in CONTRIBUTING.md
diff: Make sure you have installed:
  -- [`node.js`](https://nodejs.org/)
  +- [`node.js`](https://nodejs.org/) v10
  - `npm`
  -- the [`tslint`](https://marketplace.visualstudio.com/items?itemName=ms-vscode.vscode-typescript-tslint-plugin) extension for VS Code (recommended)
  +- the [`eslint`](https://marketplace.visualstudio.com/items?itemName=dbaeumer.vscode-eslint) extension for VS Code (recommended)
  Then run
  