Entries: collapsible: Fixed a typo in the example code for "Providing pre-rendered markup" (1-4 branch).

This is simple pull request.
I think that "arrow-d" of https://github.com/jquery/api.jquerymobile.com/blob/1-4/entries/collapsible.xml#L108 is a typo.
So I changed "arrow-d" to "arrow-r".