title: dygraphs default x-axis range
body: <p>The default Dygraphs x-axis range seems to be [first x-value, last x-value] rather than [minimum x-value, maximum x-value]. Is this deliberate? I haven't seen anything that says your input data must be sorted, nor have I found any way of setting the x-axis range like "valueRange" does for y-axes.</p>
  
  <p>Ex. input data:</p>
  
  <pre><code>[[5,1,2,3],
   [2,4,5,6],
   [3,7,8,9],
   [4,1,5,9],
   [5,5,5,5]]
  </code></pre>
  
  <p>The x-values range from [2,5], but my Dygraph always shows up with an x-axis at [5,5]. I tried setting an option as follows but it doesn't work, presumably because "valueRange" is defined for vertical height only:</p>
  
  <pre><code>{
    axes: {
      x: {
        valueRange: [2,5]
      }
    }
  }
  </code></pre>
  
  <p>For now I can go to the trouble of sorting all my input, but it would be rather more logical to change the default.</p>