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

Bumps [github.com/prometheus/client_golang](https://github.com/prometheus/client_golang) from 0.8.0 to 0.9.0.
- [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/v0.8.0...v0.9.0)

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

Gopkg.lock

@@ -258,15 +258,16 @@
   version = "v1.0.0"
 
 [[projects]]
-  digest = "1:d14a5f4bfecf017cb780bdde1b6483e5deb87e12c332544d2c430eda58734bcb"
+  digest = "1:20a8a18488bdef471795af0413d9a3c9c35dc24ca93342329b884ba3c15cbaab"
   name = "github.com/prometheus/client_golang"
   packages = [
     "prometheus",
+    "prometheus/internal",
     "prometheus/promhttp",
   ]
   pruneopts = "UT"
-  revision = "c5b7fccd204277076155f10851dad72b76a49317"
-  version = "v0.8.0"
+  revision = "1cafe34db7fdec6022e17e00e1c1ea501022f3e4"
+  version = "v0.9.0"
 
 [[projects]]
   branch = "master"

Gopkg.toml

@@ -83,7 +83,7 @@
 
 [[constraint]]
   name = "github.com/prometheus/client_golang"
-  version = "=0.8.0"
+  version = "=0.9.0"
 
 [[constraint]]
   name = "github.com/sirupsen/logrus"