replaced REACT_APP_CONFIG with APP_CONFIG

docs/latest/essentials/configuration.md

@@ -8,9 +8,9 @@
 
 The configuration for our project is in the `/public/config` directory. Our
 build process knows which configuration file to use based on the
-`REACT_APP_CONFIG` environment variable. By default, its value is
+`APP_CONFIG` environment variable. By default, its value is
 [`default.js`](https://github.com/OHIF/Viewers/blob/react/public/config/default.js).
-When we build, the `%REACT_APP_CONFIG%` value in
+When we build, the `%APP_CONFIG%` value in
 our[`/public/index.html`](https://github.com/OHIF/Viewers/blob/react/public/index.html#L12-L15)
 file is substituted for the correct configuration file's name. This sets the
 `window.config` equal to our configuration file's value.
@@ -44,13 +44,13 @@ window.config = {
 ```
 
 You can also create a new config file and specify its path relative to the build
-output's root by setting the `REACT_APP_CONFIG` environment variable. You can
+output's root by setting the `APP_CONFIG` environment variable. You can
 set the value of this environment variable a few different ways:
 
 - [Add a temporary environment variable in your shell](https://facebook.github.io/create-react-app/docs/adding-custom-environment-variables#adding-temporary-environment-variables-in-your-shell)
 - [Add environment specific variables in `.env` file(s)](https://facebook.github.io/create-react-app/docs/adding-custom-environment-variables#adding-development-environment-variables-in-env)
 - Using the `cross-env` package in an npm script:
-  - `"build": "cross-env REACT_APP_CONFIG=config/my-config.js react-scripts build"`
+  - `"build": "cross-env APP_CONFIG=config/my-config.js react-scripts build"`
 
 After updating the configuration, `yarn run build:web` to generate updated build
 output.