title: kendo ui dataviz chart aggregate includes data from wrong month
body: <p>I'm building a basic line chart in Kendo UI Dataviz and I'm having a problem with the aggregation method. The goal is to group my sales data by month and aggregate the Sum(Amount) which seems to work in my chart but I'm experiencing a bug that causes data from the first day of October to be included in the sum for September. Oct 2 shows in October but Oct 1 is included in September's total. </p>
  
  <p>The data is:</p>
  
  <p>10/1/2013 12:00:00 AM, 22964.5000</p>
  
  <p>10/2/2013 12:00:00 AM, 6762.9400</p>
  
  <pre><code>Html.Kendo().Chart(Model)
      .Name("revenue")
      .Title("Revenue Activity by Month")
      .Legend(legend =&gt; legend
          .Position(ChartLegendPosition.Bottom)
      )
      .Series(series =&gt;
              {
                  series.Area(s =&gt; s.TotalRevenue, categoryExpression: model =&gt; model.Date).Aggregate(ChartSeriesAggregate.Sum).Name("Total Revenue").Color("#73c100");
                  series.Line(s =&gt; s.RevenueSubscriber, categoryExpression: model =&gt; model.Date).Aggregate(ChartSeriesAggregate.Sum).Name("Subscriber Revenue");
                  series.Line(s =&gt; s.RevenueNonSubscriber, categoryExpression: model =&gt; model.Date).Aggregate(ChartSeriesAggregate.Sum).Name("Non-Subscriber Revenue");
              })
      .CategoryAxis(axis =&gt; axis.Date()
          .BaseUnit(ChartAxisBaseUnit.Months)
      )
      .ValueAxis(axis =&gt; axis
          .Numeric("revenue")
          .Labels(labels =&gt; labels.Format("{0:C}"))
          .Line(line =&gt; line.Visible(false))
      )
      .Tooltip(tooltip =&gt; tooltip
          .Visible(true)
          .Format("{0:C}")
      )
  </code></pre>
  
  <p>What I receive is a chart with two points on the X Axis. The first point is Sept 2013 and includes $22,964. The second point is Oct 2013 and includes $6,762. </p>