add dep

Author: Massimiliano Pippi

Diff for: go.mod

@@ -36,6 +36,7 @@ require (
 	github.com/sirupsen/logrus v1.4.2
 	github.com/smartystreets/goconvey v0.0.0-20190330032615-68dc04aab96a // indirect
 	github.com/spf13/cobra v0.0.5
+	github.com/spf13/viper v1.3.2
 	github.com/stretchr/objx v0.2.0 // indirect
 	github.com/stretchr/testify v1.4.0
 	go.bug.st/cleanup v1.0.0