Update module prometheus/client_golang to v1.9.0

go.mod

@@ -16,7 +16,7 @@ require (
 	github.com/lunixbochs/struc v0.0.0-20200707160740-784aaebc1d40
 	github.com/miscreant/miscreant.go v0.0.0-20200214223636-26d376326b75
 	github.com/openzipkin/zipkin-go v0.2.2
-	github.com/prometheus/client_golang v1.5.1
+	github.com/prometheus/client_golang v1.9.0
 	github.com/russross/blackfriday/v2 v2.0.1
 	github.com/shurcooL/sanitized_anchor_name v1.0.0 // indirect
 	github.com/theckman/go-flock v0.7.1