update uploadcare plugin

git-svn-id: https://plugins.svn.wordpress.org/uploadcare/trunk@997908 b8457f37-d9ea-0310-8a92-e5e31aec5664
add authors.txt

git-svn-id: https://plugins.svn.wordpress.org/uploadcare/trunk@997910 b8457f37-d9ea-0310-8a92-e5e31aec5664