title: Vertical lines on hover in google charts
body: <p>I am working with google line charts and angularjs directive in my project, I am searching how to get vertical lines on hover like <a href="https://trends.google.com/trends/explore?q=angular" rel="nofollow noreferrer">Google Trends</a> instead put a fixed lines, but I can't find how to do this.</p>
  
  <p>This is that I want trying to do:</p>
  
  <p><a href="https://i.stack.imgur.com/3BGDA.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3BGDA.jpg" alt="enter image description here"></a></p>
  
  <p>I just got hide vertical lines but not show on mouse hover, this is my options for angular-google-chart directive</p>
  
  <pre><code>options: {
    vAxis: {
      title: 'My title',
      gridlines: {
        count: 10
      }
    },
    hAxis: {
      title: 'title hAxis',
      gridlines: {
        color: 'transparent'
      }
    }
  }
  </code></pre>