Updated readme.txt.

git-svn-id: https://plugins.svn.wordpress.org/wp-spamshield/trunk@970025 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fixed error in readme.txt.

git-svn-id: https://plugins.svn.wordpress.org/wp-spamshield/trunk@970030 b8457f37-d9ea-0310-8a92-e5e31aec5664