Update jquery-ui-1.10.3.custom.css

IE 10 seems to require the direction keyword 'to' in the linear-gradient which looks to be the new syntax being adopted.
http://stackoverflow.com/questions/2621632/is-there-an-official-standard-css3-gradient-syntax
Merge pull request #210 from aerichmond/patch-1

Update jquery-ui-1.10.3.custom.css