title: Highcharts Line Area chart data formatting issue
body: <p>I am using Laravel backend to generate a raw data array for Highcharts. I am using <a href="http://www.highcharts.com/demo/line-time-series" rel="nofollow">this Highcharts example</a> as the basis.I cannot get my chart to format the x axis date nor the tooltip to show the correct date (like the example). I think my problem is in the data format.</p>
  
  <p><a href="http://jsfiddle.net/TheRealPapa/x5kpLxy0/" rel="nofollow">FIDDLE HERE</a></p>
  
  <p>My Laravel controller code:</p>
  
  <pre><code>$transactionData = Transaction::where('type', '=', 'INVOICE')
      -&gt;whereNotIn('status', ['DRAFT', 'CANCELLED'])
      -&gt;where('issue_date', '&gt;=', $fiscal_start)
      -&gt;orderBy('due_date', 'asc')
      -&gt;select(['issue_date', 'amount_transaction_total'])
      -&gt;get()-&gt;toArray();
  
  $invoicedLineChartData = [];
  foreach ($transactionData as $data) {
      $invoicedLineChartData[] = [
          Carbon::parse($data['issue_date']), 
          floatval($data['amount_transaction_total']))
      ];
  }
  </code></pre>
  
  <p>This generates data that looks like this:</p>
  
  <pre><code>[[{"date":"2016-07-04 01:11:07.000000","timezone_type":3,"timezone":"UTC"},909],
   [{"date":"2016-07-04 01:11:07.000000","timezone_type":3,"timezone":"UTC"},1988]...]
  </code></pre>
  
  <p>I can see from the Highcharts example that the AJAX returns data that looks like this:</p>
  
  <pre><code>[[Date.UTC(2013,5,2),0.7695],
  [Date.UTC(2013,5,3),0.7648],
  [Date.UTC(2013,5,4),0.7645],...]
  </code></pre>
  
  <p>What is the correct way to format the data on the back end for this Highchart type from Laravel side? I have tried various Carbon formats but the result is still not correct. </p>
  
  <p>Additionally, why does the y axis start at -500 when there are no negative entries in the data? Thanks!</p>