Hotfix to default locale to en_US

git-svn-id: https://plugins.svn.wordpress.org/scan-to-login/trunk@857761 b8457f37-d9ea-0310-8a92-e5e31aec5664
tagging hotfix version 1.8.1

git-svn-id: https://plugins.svn.wordpress.org/scan-to-login/trunk@857766 b8457f37-d9ea-0310-8a92-e5e31aec5664