change functiopn to check if it is an internet explorer

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7-datepicker-fix/trunk@771612 b8457f37-d9ea-0310-8a92-e5e31aec5664
New Version

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7-datepicker-fix/trunk@771613 b8457f37-d9ea-0310-8a92-e5e31aec5664