* add react-testing-library documentation/examples

* make react-testing-library a heading

* fix typo

 - react-dev-utils@5.0.1
 - react-scripts@1.1.4

 - react-scripts@1.1.3

 - react-scripts@1.1.2

Add troubleshooting for an issue that has to do with either 2FA, or using Windows, or both, when trying to deploy an app via gh-pages

Support for .mjs files added in #3239 did not account for npm libraries which ship native mjs files alongside js files. This accounts for this by ensuring .js files resolve before their accompanying .mjs file. Note that this is not an ideal end state since selecting a .mjs over a .js extension should be the result of whether `import` was used instead of `require()` in a node environment with native ESM support (currently via `--experimental-modules`). Instead, this change just *always* selects a .js extension before the .mjs extension if it exists.

This unbreaks support for using GraphQL (relay, apollo, etc) within create-react-app projects.

 - create-react-app@1.5.2
 - react-scripts@1.1.1

This reverts commit bab2c295.

I meant to apply it to `next` instead.

Update User Guide's README.md to include `json` and `css`
files in the command to format the entire project for the first time
with prettier, that it's consistent with the `lint-staged` command.

 - babel-preset-react-app@3.1.1
 - create-react-app@1.5.0
 - eslint-config-react-app@2.1.0
 - react-dev-utils@5.0.0
 - react-error-overlay@4.0.0
 - react-scripts@1.1.0

* Add warning when HOST environment variable is set (#3719)

* Improve HOST environment variable warning message

* Adjust text and message

Closes #3719

* Always include destructuring transform

* Fix lint

* fix #2223 - [feature] Implement dotenv-expand to accept variable expansion in dot env files

* add to README TOC

* fix readme

* Update README.md

* Better documentation for setupTests.js when ejecting

When running `npm run eject` before creating `src/setupTests.js`, the resulting `package.json` file, won't contain any entry for it - and this is correct in my opinion, since otherwise Jest will crash - but it's useful to have it documented and avoid pointless waste of time.

* Added additional note about src/setupTests.js

Added another note about src/setupTests.js and `npm run eject` in Testing Components section

* Update README.md

* Update README.md

'more' and 'simpler' together is incorrect.

* add support to set REACT_EDITOR to none

* change README message

* change condition to avoid problems with editor being null

* move condition to avoid extra code

* Update README.md with a note that reminds users to prepend REACT_APP_ to their environment variables. 
* Based on #865, where Dan Abramov suggests the person who filed the issue create a PR with these changes.
* Took the language from [Adding Custom Environment Variables](https://github.com/facebookincubator/create-react-app/tree/master/packages/react-scripts/template#adding-custom-environment-variables)