Fix build file to point at correct URL

Summary:
This should get talk-throughs working in Opera (don't have John's local recordings data yet).
Opera didn't like // in the URL and 404ed instead of finding the SWF file.

Test Plan: - Load talkthroughs in Opera, don't see 404 for the SoundManager URL

Reviewers: alexrodrigues, john

Reviewed By: john

Subscribers: john, #cs

Differential Revision: http://phabricator.khanacademy.org/D13871