title: Rails chartkick stacked bar charts
body: <p>I'm trying to create a stacked bar chart using Rails <a href="https://github.com/ankane/chartkick" rel="noreferrer">Chartkick</a> gem and I'm using Google charts API.</p>
  
  <p>I have use this line to generate the bar chart using chartkick.</p>
  
  <pre><code>&lt;%= bar_chart data, :library =&gt; {:isStacked =&gt; true} %&gt; 
  </code></pre>
  
  <p>But what i'm getting is a simple bar chart not a stacked one.My question is what is the structure of the data which i should pass to <code>data</code> parameter. I have try passing an array, like(from google charts samples)</p>
  
  <pre><code>[['Genre', 'Fantasy &amp; Sci Fi', 'Romance', 'Mystery/Crime', 'General','Western', 'Literature', { role: 'annotation' } ],['2010', 10, 24, 20, 32, 18, 5, '']]
  </code></pre>
  
  <p>but it didn't work.</p>