Bump CircleCI orb

Update CircleCI orb to latest.

Signed-off-by: SuperQ <superq@gmail.com>

Author: SuperQ

.circleci/config.yml

@@ -1,7 +1,7 @@
 ---
 version: 2.1
 orbs:
-  prometheus: "prometheus/prometheus@0.17.1"
+  prometheus: "prometheus/prometheus@0.18.0"
 executors:
   # Whenever the Go version is updated here, .promu.yml should also be updated.
   golang: