title: Webpack workbox Can't find self.__WB_MANIFEST in your SW source
body: <p>I migrate from v4 to v5 of webpack-workbox-plugin but when I try to build, I got error:</p>
  
  <pre class="lang-sh prettyprint-override"><code>ERROR in Can't find self.__WB_MANIFEST in your SW source.
  Child InjectManifest:
      Asset     Size  Chunks             Chunk Names
      sw.js  1.5 KiB       0  [emitted]  InjectManifest
  Child html-webpack-plugin for "index.html":
       1 asset
  </code></pre>
  
  <p>Do <code>__WB_MANIFEST</code> will create in a precach-manifest file and import automatically like v4?</p>
  
  <p>WebpackConfig :</p>
  
  <pre class="lang-js prettyprint-override"><code>new WorkboxPlugin.InjectManifest({
        swSrc: 'sw.js',
        chunks: ['*.chunk.js'],
        exclude: [/\.(?:png|jpg|jpeg|svg)$/, /\.map$/, /manifest\.json$/, /service-worker\.js$/, /sw\.js$/],
        include: [path.resolve(process.cwd(), 'build')],
      }),
  </code></pre>
  
  <p>My sw.js:</p>
  
  <pre class="lang-js prettyprint-override"><code>
  importScripts('./ChabokSDKWorker.js', 'https://storage.googleapis.com/workbox-cdn/releases/5.0.0/workbox-sw.js');
  
  /* eslint-disable no-undef */
  
  if (workbox) {
    workbox.core.skipWaiting();
    workbox.core.clientsClaim();
    workbox.precaching.cleanupOutdatedCaches();
  
    // eslint-disable-next-line no-restricted-globals,no-underscore-dangle
    workbox.precaching.precacheAndRoute(self.__WB_MANIFEST);
  
    // java-script files cache
    workbox.routing.registerRoute(
      new RegExp('.+\\.js$'),
      workbox.strategies.StaleWhileRevalidate({
        cacheName: 'js-cache',
        plugins: [
          new workbox.expiration.Plugin({
            maxEntries: 20,
            maxAgeSeconds: 60 * 60 * 24 * 7,
            purgeOnQuotaError: true,
          }),
          new workbox.cacheableResponse.Plugin({
            statuses: [0, 200],
          }),
        ],
      }),
    );
  
    // css files cache
    workbox.routing.registerRoute(
      new RegExp('.+\\.css$'),
      workbox.strategies.StaleWhileRevalidate({
        cacheName: 'css-cache',
        plugins: [
          new workbox.expiration.Plugin({
            maxEntries: 5,
            maxAgeSeconds: 60 * 60 * 24 * 7,
            purgeOnQuotaError: true,
          }),
          new workbox.cacheableResponse.Plugin({
            statuses: [0, 200],
          }),
        ],
      }),
    );
  
    // image files cache
    workbox.routing.registerRoute(
      new RegExp('.+\\.(png|jpg|jpeg|svg)$'),
      workbox.strategies.CacheFirst({
        cacheName: 'images-cache',
        plugins: [
          new workbox.expiration.Plugin({
            maxEntries: 20,
            maxAgeSeconds: 60 * 60 * 24 * 7,
            purgeOnQuotaError: true,
          }),
          new workbox.cacheableResponse.Plugin({
            statuses: [0, 200],
          }),
        ],
      }),
    );
  
    workbox.routing.registerRoute(
      new RegExp('/.*'),
      workbox.strategies.NetworkFirst({}),
      'GET',
    );
  } else {
    console.log(`Boo! Workbox didn't load `);
  }
  /* eslint-enable no-undef */
  </code></pre>