title: chartkick why is x-axis a date
body: <p>I've created a custom hash but the x-axis is showing up as a date. I want it to just show the value in the hash (1,2,3 etc...). This is my first time using chartkick so I'm lost as to why this is happening.  </p>
  
  <p>What's being displayed is January 1, 2000 with the value of 504, February 1, 2000 with value of 499, March 1 etc....</p>
  
  <p>When I set @chart_hash as an array, instead of a hash (which is what is shown below), I get times in the x-axis instead of dates.</p>
  
  <p>application.html.erb</p>
  
  <pre><code>&lt;head&gt;
  &lt;title&gt;SampleApp&lt;/title&gt;
    &lt;%= javascript_include_tag "//www.google.com/jsapi", "chartkick" %&gt;
    &lt;%= stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track' =&gt; true %&gt;
    &lt;%= javascript_include_tag 'application', 'data-turbolinks-track' =&gt; true %&gt;
    &lt;%= csrf_meta_tags %&gt;
  &lt;/head&gt;
  </code></pre>
  
  <p>_chart.html.erb</p>
  
  <pre><code>&lt;%= line_chart @chart_hash %&gt;
  </code></pre>
  
  <p>@chart_hash</p>
  
  <pre><code>{0=&gt;504, 1=&gt;499, 2=&gt;499, 3=&gt;504, 4=&gt;509, 5=&gt;514, 6=&gt;514, 7=&gt;521.5, 8=&gt;516, 9=&gt;511, 10=&gt;511, 11=&gt;511, 12=&gt;506, 13=&gt;501, 14=&gt;501, 15=&gt;506, 16=&gt;511, 17=&gt;516, 18=&gt;511, 19=&gt;518.5, 20=&gt;522.5}
  </code></pre>