small bug fix

git-svn-id: https://plugins.svn.wordpress.org/mymail-cool-captcha/trunk@890155 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update

git-svn-id: https://plugins.svn.wordpress.org/mymail-cool-captcha/trunk@890156 b8457f37-d9ea-0310-8a92-e5e31aec5664