typo in readme.txt

git-svn-id: https://plugins.svn.wordpress.org/wp-forecast/trunk@989865 b8457f37-d9ea-0310-8a92-e5e31aec5664
typo in readme.txt

git-svn-id: https://plugins.svn.wordpress.org/wp-forecast/trunk@989867 b8457f37-d9ea-0310-8a92-e5e31aec5664