translation string tweak

git-svn-id: https://plugins.svn.wordpress.org/ewww-image-optimizer/trunk@1056470 b8457f37-d9ea-0310-8a92-e5e31aec5664
another translation string tweak

git-svn-id: https://plugins.svn.wordpress.org/ewww-image-optimizer/trunk@1056471 b8457f37-d9ea-0310-8a92-e5e31aec5664