Close after switch branch

Related to https://github.com/zaggino/brackets-git/issues/222

I've added the requested feature (just a draft) but the GitCli function doesn't work, I need help to understand what am I doing wrong.

This is the bugged code (I think):

    function getDeletedFiles(oldBranch, newBranch) {
        return git(["diff", "--name-status", oldBranch + "--" + newBranch])
            .then(function (stdout) {
                console.log("getDeletedFiles response", stdout);
                return stdout.split("\n").map(function (row) {
                    row.substring(1).trim();
                });
            })
            .catch(function () {
                return null;
            });
    }

Thanks.