status-heatmap-plugin for Grafana

- fixes for 5.1.3
- nulls as empty

src/libs/d3-scale-chromatic/ramp.js

@@ -0,0 +1,5 @@
+import d3 from 'd3';
+
+export default function(scheme) {
+  return d3.interpolateRgbBasis(scheme[scheme.length - 1]);
+}