title: NVD3 Line Chart X Axis Ticks Are Missing
body: <p>I am using NVD3 to display line chart here: <a href="http://jsbin.com/xodaxafiti/2/edit?js,output" rel="noreferrer">http://jsbin.com/xodaxafiti/2/edit?js,output</a></p>
  
  <p>But it seems like NVD3 auto-hide some tickLabels on XAxis, but only those ticks near the edge, i.e. 2-3Oct and 27-28Oct (except the first and last tick). I know that this is an auto-reduce because when I increase the width of chart, the ticks start to show up. However I find that this reducing behaviour weird, and the lineChart does not have reduceXTicks option like multiBarChart.</p>
  
  <p>I want to be able to control the reducing behaviour myself like <a href="https://github.com/novus/nvd3/issues/70" rel="noreferrer">this</a>:</p>
  
  <pre><code>var chart = nv.models.lineChart()       
     .useInteractiveGuideline(true)
     .margin({left: 80,top: 20,bottom: 120,right: 20});  
  
  chart.xAxis.ticks(function() {
     return data[0].map(chart.x()).filter(function(d,i) {
        i % Math.ceil(data[0].values.length / (availableWidth / 100)) === 0;
     })
  })
  </code></pre>
  
  <p>But it didn't work. Anyone has any idea how to control this?</p>
  
  <p><img src="https://i.stack.imgur.com/SWACh.png" alt="missing tickLabels"></p>