Restore the use of cobra.OnInitialize in cobra executable

Without cobra.OnInitialize, cobra does not see the --config
command-line option and always tries to load $HOME/.cobra.yaml
instead.

cobra/cmd/root.go

@@ -40,7 +40,7 @@ func Execute() {
 }
 
 func init() {
-	initViper()
+	cobra.OnInitialize(initConfig)
 
 	rootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is $HOME/.cobra.yaml)")
 	rootCmd.PersistentFlags().StringP("author", "a", "YOUR NAME", "author name for copyright attribution")
@@ -55,7 +55,7 @@ func init() {
 	rootCmd.AddCommand(initCmd)
 }
 
-func initViper() {
+func initConfig() {
 	if cfgFile != "" {
 		// Use config file from the flag.
 		viper.SetConfigFile(cfgFile)