Change RDD cache color to red (minor)

Author: Andrew Or

core/src/main/resources/org/apache/spark/ui/static/spark-dag-viz.js

@@ -53,7 +53,7 @@
 
 var VizConstants = {
   rddColor: "#444444",
-  rddCachedColor: "#7DDD00",
+  rddCachedColor: "#FF0000",
   rddOperationColor: "#AADFFF",
   stageColor: "#FFDDEE",
   clusterLabelColor: "#888888",