Use npm script hooks to avoid && in deploy script (#1324)

packages/react-scripts/scripts/build.js

@@ -181,7 +181,8 @@ function build(previousSizeMap) {
         console.log('    ' + chalk.dim('// ...'));
         console.log('    ' + chalk.yellow('"scripts"') + ': {');
         console.log('      ' + chalk.dim('// ...'));
-        console.log('      ' + chalk.yellow('"deploy"') + ': ' + chalk.yellow('"npm run build&&gh-pages -d build"'));
+        console.log('      ' + chalk.yellow('"predeploy"') + ': ' + chalk.yellow('"npm run build",'));
+        console.log('      ' + chalk.yellow('"deploy"') + ': ' + chalk.yellow('"gh-pages -d build"'));
         console.log('    }');
         console.log();
         console.log('Then run:');

packages/react-scripts/template/README.md

@@ -1132,17 +1132,18 @@ To publish it at [https://myusername.github.io/my-app](https://myusername.github
 npm install --save-dev gh-pages
 ```
 
-Add the following script in your `package.json`:
+Add the following scripts in your `package.json`:
 
 ```js
   // ...
   "scripts": {
     // ...
-    "deploy": "npm run build&&gh-pages -d build"
+    "predeploy": "npm run build",
+    "deploy": "gh-pages -d build"
   }
 ```
 
-(Note: the lack of whitespace is intentional.)
+The `predeploy` script will run automatically before `deploy` is run.
 
 #### Step 3: Deploy the site by running `npm run deploy`