build(deps): bump github.com/spf13/viper from 1.8.0 to 1.8.1

Bumps [github.com/spf13/viper](https://github.com/spf13/viper) from 1.8.0 to 1.8.1.
- [Release notes](https://github.com/spf13/viper/releases)
- [Commits](https://github.com/spf13/viper/compare/v1.8.0...v1.8.1)

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

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

go.mod

@@ -22,7 +22,7 @@ require (
 	github.com/opentracing/opentracing-go v1.2.0
 	github.com/rs/zerolog v1.23.0
 	github.com/spf13/cobra v1.1.3
-	github.com/spf13/viper v1.8.0
+	github.com/spf13/viper v1.8.1
 	github.com/stretchr/testify v1.7.0
 	github.com/tonistiigi/fsutil v0.0.0-20201103201449-0834f99b7b85
 	github.com/tonistiigi/units v0.0.0-20180711220420-6950e57a87ea