Change Workbench Demo browser view URL

The old URL (to Birt demo) is not displayed anymore due to
X-Frame-Options set on response to DENY. This is the case for all pages
hosted on eclipse.org domain including RAP home page.

Change browser view URL to http://xkcd.com.

444331: [Demo] Browser View is empty
https://bugs.eclipse.org/bugs/show_bug.cgi?id=444331

Change-Id: Ib2a2e2eba2fca7df19d53d2088a6d736ef861f01
Signed-off-by: Ivan Furnadjiev <ivan@eclipsesource.com>