Bump github.com/spf13/viper from 1.8.1 to 1.9.0 (#320)

Bumps [github.com/spf13/viper](https://github.com/spf13/viper) from 1.8.1 to 1.9.0.
- [Release notes](https://github.com/spf13/viper/releases)
- [Commits](spf13/viper@v1.8.1...v1.9.0)

---
updated-dependencies:
- dependency-name: github.com/spf13/viper
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

go.mod

@@ -26,7 +26,7 @@ require (
 	github.com/prometheus/client_golang v0.9.4
 	github.com/rcrowley/go-metrics v0.0.0-20200313005456-10cdbea86bc0
 	github.com/sirupsen/logrus v1.8.1
-	github.com/spf13/viper v1.8.1
+	github.com/spf13/viper v1.9.0
 	github.com/stretchr/testify v1.7.0
 	github.com/vmihailenco/msgpack/v4 v4.3.11
 	google.golang.org/grpc v1.40.0