Bump version number to 2.8.1

git-svn-id: https://plugins.svn.wordpress.org/visual-form-builder/trunk@892011 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update wrong filename in a date picker translation i18n

git-svn-id: https://plugins.svn.wordpress.org/visual-form-builder/trunk@892013 b8457f37-d9ea-0310-8a92-e5e31aec5664