capgen: fix build, add "lang" flag.
capgen: fix build, add "lang" flag.

msn217/captcha,zj8487/captcha,rainyear/captcha,kaz8/go-captcha,eleme/fork_captcha,ZiRo-/captcha,dchest/captcha,ZiRo-/captcha,thomasmodeneis/captcha,oblank/captcha,gotomypc/captcha