Silence PHP Warning: unlink() in GC

[Miroslav Fedeleš]

Sometimes I get: PHP Warning: unlink() due to concurrent requests on server. Thus unlink($file->getPathname()); in method \Zend\Captcha\Image::gc() should be silenced with: @unlink($file->getPathname());.

[Abdul Malik Ikhsan]

@fedys I've created PR #23 for it.

[Miroslav Fedeleš]

@samsonasik Thanks ;)