Increase jitter cap to 30 seconds

This is a quick fix until PR prometheus-community#82 [0] has landed upstream.

[0]: prometheus-community#82

cmd/client/main.go

@@ -212,7 +212,7 @@ func newJitter() decorrelatedJitter {
 	rand.Seed(time.Now().UnixNano())
 	return decorrelatedJitter{
 		min: 50 * time.Millisecond,
-		cap: 5 * time.Second,
+		cap: 30 * time.Second,
 	}
 }