Need to include branch name

[aaronchantrill]

When cloning a repository, we are assuming the default branch is what we want. When updating a repository, though, we are assuming the "master" branch. Most new Github repositories now use a "main" branch rather than "master" which is causing problems when attempting to update plugins, and we should not assume that the user is attempting to submit their default branch anyway. To fix this, we should add a "branch" field.