Update loadSwitchFiles to reference main branch

[dotproto]

Issue #49 notes that the List of Command Line Switches page states that the "Last automated update occurred on 2020-08-12". @confor posited in this comment that this may be because Chromium switched from master to main.

While this doesn't quite align with the cutover dates outlined in this dev-infra thread, it seemed like it might still be a good idea to update the branch referenced in loadSwitchFiles().

[beverloo]

Thanks :) I'll merge this - the remaining issue for the breakage is that my VPS no longer has enough memory to complete the git checkout (or update), which is a bit surprising as the VM has 4 GiB of RAM. I've requested an upgrade to 8 GiB to get this rolling again.