Sparklines should scale to the data range (#12010)

* Add a full range option to sparklines

* line zero=false

public/app/plugins/panel/singlestat/module.ts

@@ -580,6 +580,7 @@ class SingleStatCtrl extends MetricsPanelCtrl {
           lines: {
             show: true,
             fill: 1,
+            zero: false,
             lineWidth: 1,
             fillColor: panel.sparkline.fillColor,
           },