Update module github.com/prometheus/client_golang to v1.12.0 (oliver006#603)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

go.mod

@@ -4,7 +4,7 @@ go 1.13
 
 require (
 	github.com/gomodule/redigo v1.8.8
-	github.com/prometheus/client_golang v1.11.0
+	github.com/prometheus/client_golang v1.12.0
 	github.com/mna/redisc v1.3.2
 	github.com/prometheus/client_model v0.2.0
 	github.com/sirupsen/logrus v1.8.1