Update https://github.com/urfave/cli to version 1.2.0 (#6838)

From un-tagged pervious version : https://github.com/urfave/cli/compare/d86a009f5e13...master

vendor/github.com/urfave/cli/cli.go

@@ -12,6 +12,7 @@
 //     app.Usage = "say a greeting"
 //     app.Action = func(c *cli.Context) error {
 //       println("Greetings")
+//       return nil
 //     }
 //
 //     app.Run(os.Args)