use https for amara integration

Currently you get a warning when you click the "Go to subtitle creation
tool" button because you are posting a form to an HTTP URL from an HTTPS
one (Canvas). This should fix that warning.

Test plan:

 - On an uploaded video, click the subtitle tool and choose "Upload
   subtitles"
 - On the popup, click "Go to subtitle creation tool"
 - There should be no warning message shown

Change-Id: I1743399d8a2ceb07740b8ca5948ea2741aa99594
Reviewed-on: https://gerrit.instructure.com/45077
Reviewed-by: Brian Palmer <brianp@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Paul Hinze <paulh@instructure.com>