compare ring sum within epsilon of 1

fixes #1661
closes #1662

src/sunburst-chart.js

@@ -489,7 +489,7 @@ dc.sunburstChart = function (parent, chartGroup) {
             }
 
             var portionsSum = d3.sum(relativeSizes);
-            if (portionsSum !== 1) {
+            if (Math.abs(portionsSum - 1) > dc.constants.NEGLIGIBLE_NUMBER) {
                 throw new dc.errors.BadArgumentException(
                     'relativeRingSizes : portions must add up to 1, but sum was ' + portionsSum);
             }