Update shotcut to 20.09.13
This is the full release version of 20.09.01, which was a prerelease. Going forward, only stable releases will be pushed.
Full release notes are available here.
Test Plan: Create a new project, add a clip, modify it, export to MP4
Reviewers: Triage Team, JoshStrobl
Reviewed By: Triage Team, JoshStrobl
Differential Revision: https://dev.getsol.us/D9654