add alias for helm up for helm update

cmd/helm/update.go

@@ -19,6 +19,7 @@ var verboseUpdate bool
 
 var updateCommand = &cobra.Command{
 	Use:     "update",
+	Aliases: []string{"up"},
 	Short:   "Update information on available charts in the chart repositories.",
 	RunE:    runUpdate,
 }