Update example config file from json to new protobuf format.

Change-Id: I38646c2be53b6993abe464d9cdd9b211678de496

documentation/examples/prometheus.conf

@@ -1,24 +1,26 @@
 global {
-  scrape_interval = "1s"
-  evaluation_interval = "1s"
+  scrape_interval: "1s"
+  evaluation_interval: "1s"
   labels {
-    monitor = "test"
+    label {
+      name: "owner"
+      value: "test"
+    }
   }
-  rule_files = [
-    "prometheus.rules"
-  ]
+  rule_file: "prometheus.rules"
 }
 
 job {
-  name = "prometheus"
-  scrape_interval = "5s"
+  name: "prometheus"
+  scrape_interval: "5s"
 
-  targets {
-    endpoints = [
-      "http://localhost:9090/metrics.json"
-    ]
+  target_group {
+    target: "http://localhost:9090/metrics.json"
     labels {
-      group = "canary"
+      label {
+        name: "group"
+        value: "canary"
+      }
     }
   }
 }