Bump github.com/spf13/viper from 1.7.1 to 1.8.1

Bumps [github.com/spf13/viper](https://github.com/spf13/viper) from 1.7.1 to 1.8.1.
- [Release notes](https://github.com/spf13/viper/releases)
- [Commits](spf13/viper@v1.7.1...v1.8.1)

---
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>

go.mod

@@ -6,14 +6,13 @@ require (
 	bou.ke/monkey v1.0.2
 	github.com/pkg/errors v0.9.1
 	github.com/prometheus/client_golang v1.11.0
-	github.com/spf13/viper v1.7.1
+	github.com/spf13/viper v1.8.1
 	github.com/stretchr/testify v1.7.0
 	go.uber.org/atomic v1.9.0
 	go.uber.org/dig v1.11.0
 	go.uber.org/zap v1.18.1
-	golang.org/x/net v0.0.0-20200625001655-4c5254603344
-	golang.org/x/tools v0.0.0-20200103221440-774c71fcf114 // indirect
-	google.golang.org/grpc v1.37.0
+	golang.org/x/net v0.0.0-20210405180319-a5a99cb37ef4
+	google.golang.org/grpc v1.38.0
 )
 
 // Blocked in Russia