title: chartkick how to pass hAxis.format to the underlying library
body: <p>I know you can use the :library=>{:pointSize=>0} syntax to pass options to the underlying charting library (Google charts in my case). </p>
  
  <p>However, I can't figure out how to set the hAxis.format option. I've tried </p>
  
  <pre><code>&lt;%= line_chart(@chart_data, :library=&gt;{:pointSize =&gt; 0, :hAxis =&gt; "{format: 'yyyy-mm-dd'}"}, :min =&gt; @vmin, :max =&gt; @vmax) %&gt;
  </code></pre>
  
  <p>and </p>
  
  <pre><code>&lt;%= line_chart(@chart_data, :library=&gt;{:pointSize =&gt; 0, :hAxis.format =&gt; "yyyy-mm-dd"}, :min =&gt; @vmin, :max =&gt; @vmax) %&gt;
  </code></pre>
  
  <p>Both ways result in errors. What's the proper syntax for this?</p>