build(deps): bump github.com/prometheus/client_golang

Bumps [github.com/prometheus/client_golang](https://github.com/prometheus/client_golang) from 0.9.0 to 0.9.1.
- [Release notes](https://github.com/prometheus/client_golang/releases)
- [Changelog](https://github.com/prometheus/client_golang/blob/master/CHANGELOG.md)
- [Commits](https://github.com/prometheus/client_golang/compare/v0.9.0...v0.9.1)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Gopkg.lock

@@ -258,7 +258,7 @@
   version = "v1.0.0"
 
 [[projects]]
-  digest = "1:20a8a18488bdef471795af0413d9a3c9c35dc24ca93342329b884ba3c15cbaab"
+  digest = "1:26663fafdea73a38075b07e8e9d82fc0056379d2be8bb4e13899e8fda7c7dd23"
   name = "github.com/prometheus/client_golang"
   packages = [
     "prometheus",
@@ -266,8 +266,8 @@
     "prometheus/promhttp",
   ]
   pruneopts = "UT"
-  revision = "1cafe34db7fdec6022e17e00e1c1ea501022f3e4"
-  version = "v0.9.0"
+  revision = "abad2d1bd44235a26707c172eab6bca5bf2dbad3"
+  version = "v0.9.1"
 
 [[projects]]
   branch = "master"

Gopkg.toml

@@ -83,7 +83,7 @@
 
 [[constraint]]
   name = "github.com/prometheus/client_golang"
-  version = "=0.9.0"
+  version = "=0.9.1"
 
 [[constraint]]
   name = "github.com/sirupsen/logrus"