title: get "ReferenceError: playwright is not defined" when using playwright.config.js
body: <p>My very first day trying Playwright and I am having trouble using config. My steps:</p>
  <ol>
  <li>init project and install</li>
  </ol>
  <pre><code>npm init
  npm i -D @playwright/test --save
  npx playwright install 
  </code></pre>
  <ol start="2">
  <li>create tests/foo.spec.js</li>
  </ol>
  <pre><code>const { test, expect } = require('@playwright/test');
  
  test('basic test', async ({ page }) =&gt; {
    await page.goto('https://playwright.dev/');
    const title = page.locator('.navbar__inner .navbar__title');
    await expect(title).toHaveText('Playwright');
  });
  </code></pre>
  <ol start="3">
  <li>run it</li>
  </ol>
  <pre><code>$ npx playwright test
    ✓  tests/foo.spec.js:3:1 › basic test (3s)
  </code></pre>
  <ol start="4">
  <li>Create playwright.config.js</li>
  </ol>
  <pre><code>// @ts-check
  const { devices } = require('@playwright/test');
  
  /** @type {import('@playwright/test').PlaywrightTestConfig} */
  const config = {
      use: {
          headless: false,
          viewport: { width: 1280, height: 720 },
          ignoreHTTPSErrors: true,
          video: 'on-first-retry',
      },
  };
  
  module.exports = config;
  </code></pre>
  <ol start="5">
  <li>run again and get error</li>
  </ol>
  <pre><code>$ npx playwright test
  Using config at /Users/me/git/left/playwright/playwright.config.js
  ReferenceError: playwright is not defined
      at Object.&lt;anonymous&gt; (/Users/me/git/left/playwright/playwright.config.js:1:1)
      at Module._compile (node:internal/modules/cjs/loader:1095:14)
  ...
  (/Users/me/git/left/playwright/node_modules/@playwright/test/lib/test/cli.js:80:7)
  </code></pre>
  <ol start="6">
  <li>Thank you for helping. My env.</li>
  </ol>
  <pre><code>playwright@1.0.0 /Users/me/git/left/playwright
  └── @playwright/test@1.15.0  
  
  $ npm -v
  7.18.1 
  
  $ node -v
  v16.4.2
  </code></pre>