title: change space between horizontal (grid) lines for line chart
body: <p>is it possible to manually change space between horizontal (grid) lines? setting <code>maintainAspectRatio: false,</code>kinda does the trick but makes the graph height too narrow. I see that there is an option to extend existing chart types</p>
  
  <pre><code>Chart.types.Line.extend({
  // Passing in a name registers this chart in the Chart namespace in the same way
  name: "LineAlt",
  initialize: function(data){
      console.log('My Line chart extension');
      Chart.types.Line.prototype.initialize.apply(this, arguments);
  }
  });
  
  // Creates a line chart in the same way
  new Chart(ctx).LineAlt(data);
  </code></pre>
  
  <p>but I dont know how to catch and change height between lines. I am new to chartjs so can it be done? any help would be much appreciated. I am trying to change height of the graph or set max-height so it does not look too big when it's responsive?</p>