title: Karma coverage istanbul does not create folder
body: <p>I am trying to integrate a code coverage reporter to my karma tests.</p>
  
  <p>I set up the following changes in my config:</p>
  
  <pre><code>coverageIstanbulReporter: {
    reports: ['html', 'lcovonly', 'text-summary'],
  
    // base output directory. If you include %browser% in the path it will be replaced with the karma browser name
    dir: path.join(__dirname, 'coverage'),
  
    // if using webpack and pre-loaders, work around webpack breaking the source path
    fixWebpackSourcePaths: true,
  },
  
  reporters: config.coverage ? ['kjhtml', 'dots', 'coverage-istanbul'] : ['kjhtml', 'dots'],
  </code></pre>
  
  <p>But unfortnetly, it does not create a <code>coverage</code> folder.</p>
  
  <p>Here is my  <a href="https://gist.github.com/AmitMY/5d84223ce2262bd2ba3a99275a78e9b6" rel="nofollow noreferrer">full karma.config.js</a></p>
  
  <p>What am I doing wrong here? Note, that I am calling <code>karma start ./karma.conf.js --coverage</code> and even checked without the config coverage parameter.</p>