fix: calculate cardWidth over max datapoints for target

- correct render of inconsistent timestamps between targets

src/rendering.js

@@ -254,6 +254,7 @@ export default function link(scope, elem, attrs, ctrl) {
     yAxisWidth = getYAxisWidth(heatmap) + Y_AXIS_TICK_PADDING;
     chartWidth = width - yAxisWidth - margin.right;
 
+    // TODO allow per-y cardWidth!
     // we need to fill chartWidth with xBucketSize cards.
     xGridSize = chartWidth / (cardsData.xBucketSize+1);
     cardWidth = xGridSize - cardHSpacing;