title: No "build" folder found when running npm run deploy
body: <p>I am trying to deploy my react app to github pages.  Every time I run "npm run deploy" I get this error:</p>
  
  <pre><code>ENOENT: no such file or directory, stat '/Users/username/my-app/build'
  
  npm ERR! Darwin 16.3.0
  npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "run" "deploy"
  npm ERR! node v6.11.0
  npm ERR! npm  v3.10.10
  npm ERR! code ELIFECYCLE
  npm ERR! reactdemo@1.0.0 deploy: `gh-pages -d build`
  npm ERR! Exit status 1
  npm ERR! 
  npm ERR! Failed at the reactdemo@1.0.0 deploy script 'gh-pages -d build'.
  npm ERR! Make sure you have the latest version of node.js and npm installed.
  npm ERR! If you do, this is most likely a problem with the reactdemo package,
  npm ERR! not with npm itself.
  npm ERR! Tell the author that this fails on your system:
  npm ERR!     gh-pages -d build
  npm ERR! You can get information on how to open an issue for this project with:
  npm ERR!     npm bugs reactdemo
  npm ERR! Or if that isn't available, you can get their info via:
  npm ERR!     npm owner ls reactdemo
  npm ERR! There is likely additional logging output above.
  </code></pre>
  
  <p>Here are my package.json scripts</p>
  
  <pre><code>"scripts": {
      "compile": "webpack",
      "test": "echo \"Error: no test specified\" &amp;&amp; exit 1",
      "build": "webpack --config webpack.config.js",
      "predeploy": "npm run build",
      "deploy": "gh-pages -d build"
    },
  </code></pre>
  
  <p>Webpack.config.js</p>
  
  <pre><code>const path = require('path');
  
  module.exports = {
    context: path.join(__dirname, 'src'),
    entry: [
      './main.js',
    ],
    output: {
      path: path.join(__dirname, 'www'),
      filename: 'bundle.js',
    },
    module: {
      rules: [
        {
          test: /\.js$/,
          exclude: /node_modules/,
          use: [
            'babel-loader',
          ],
        },
      ],
    },
    resolve: {
      modules: [
        path.join(__dirname, 'node_modules'),
      ],
    },
  };
  </code></pre>
  
  <p>I am guessing that it has something to do with the way my build script is written.  Running "npm run build" works fine.</p>
  
  <p>Edit:  Added webpack config</p>