Update DEPS roller script to use 'main'. It was still using the 'master' branch. Bug: angleproject:6700 Change-Id: I6b0d94f049b46741853ef07ba4f8f8ff7d156622 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3282687 Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>