ui-slch: Set heatmap to 6 months

Signed-off-by: Kwong Tung Nan <tungnan5636@gmail.com>

Author: kwongtn

src/app/@ui/spotting-line-calendar-heatmap/spotting-line-calendar-heatmap.component.ts

@@ -95,7 +95,7 @@ export class SpottingLineCalendarHeatmapComponent implements OnInit, OnChanges {
 
     setAndRenderChart() {
         const startDate = new Date();
-        startDate.setMonth(startDate.getMonth() - 12);
+        startDate.setMonth(startDate.getMonth() - 6);
         startDate.setDate(1);
         const startDateString = startDate.toISOString().split("T")[0];