Dependency updates. (#14033)

* Update dependencies.

* Fix tests.

vendor/github.com/spf13/cobra/go.mod

@@ -3,11 +3,10 @@ module github.com/spf13/cobra
 go 1.12
 
 require (
-	github.com/BurntSushi/toml v0.3.1 // indirect
-	github.com/cpuguy83/go-md2man v1.0.10
+	github.com/cpuguy83/go-md2man/v2 v2.0.0
 	github.com/inconshreveable/mousetrap v1.0.0
 	github.com/mitchellh/go-homedir v1.1.0
 	github.com/spf13/pflag v1.0.3
-	github.com/spf13/viper v1.3.2
+	github.com/spf13/viper v1.4.0
 	gopkg.in/yaml.v2 v2.2.2
 )