Add missing semicolons to jquery.mobile.transition.slidefade.css

I tried copying jquery.mobile.structure-1.3.0-beta.1.css to a .SCSS file to use it in a SASS project, but the .SCSS file wouldn't compile because of two missing semicolons on lines 385 and 388. These two lines come from css/structure/jquery.mobile.transition.slidefade.css. This pull request adds those two missing semicolons.