fix(git): add vendor in .gitignore

vendor/github.com/mattn/go-isatty/isatty_plan9.go

@@ -1,23 +0,0 @@
-//go:build plan9
-// +build plan9
-
-package isatty
-
-import (
-	"syscall"
-)
-
-// IsTerminal returns true if the given file descriptor is a terminal.
-func IsTerminal(fd uintptr) bool {
-	path, err := syscall.Fd2path(int(fd))
-	if err != nil {
-		return false
-	}
-	return path == "/dev/cons" || path == "/mnt/term/dev/cons"
-}
-
-// IsCygwinTerminal return true if the file descriptor is a cygwin or msys2
-// terminal. This is also always false on this environment.
-func IsCygwinTerminal(fd uintptr) bool {
-	return false
-}