CRA 2.1.8 update

[Gnito]

Create React App (CRA) 2.1.8 - Breaking changes:

Polyfills for IE 9, IE 10, and IE 11 are no longer included by default (but you can opt in!)

yarn add react-app-polyfill

Next, place one of the following lines at the very top of src/index.js:
import 'react-app-polyfill/ie9'; // For IE 9-11 support
import 'react-app-polyfill/ie11'; // For IE 11 support

Code splitting is still not included. We need to figure out some Webpack configuration for SSR before it can be introduced.

Autoprefixer is now exposed through package.json with keyword "browserlist".
The default comes from CRA:

"browserslist": {
    "production": [">0.2%", "not dead", "not op_mini all"],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  },

Previously this was:

  [
    '>1%',
    'last 4 versions',
    'Firefox ESR',
    'not ie < 9', // React doesn't support IE8 anyway
  ],

Other things to check, when updating from upstream:

• Fix z-index calculation (there was an odd calculation that worked previously)
• Plain hash-links cause errors (we used those in Button.example.js)
• Update snapshots (Jest had updated indentation on snapshots - you might need to update your snapshots)