Update cobra and pflag

Signed-off-by: Lantao Liu <lantaol@google.com>

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

@@ -11,14 +11,8 @@ import (
 
 var preExecHookFn = preExecHook
 
-// enables an information splash screen on Windows if the CLI is started from explorer.exe.
-var MousetrapHelpText string = `This is a command line tool
-
-You need to open cmd.exe and run it from there.
-`
-
 func preExecHook(c *Command) {
-	if mousetrap.StartedByExplorer() {
+	if MousetrapHelpText != "" && mousetrap.StartedByExplorer() {
 		c.Print(MousetrapHelpText)
 		time.Sleep(5 * time.Second)
 		os.Exit(1)