Adapt to new structure of jQuery UI 1.11.0

Since version v5.0.0 (https://github.com/joliss/jquery-ui-rails/commit/774f8b3e2e5ae8b80515128dd0cdb5cde48dfc01) of `jquery-ui-rails` the file naming is updated:
`jquery.ui.*.js/css` => `jquery-ui/*.js/css`