Return a boolean value for whether the given file is tracked by git.

def git_ls_files(filename):
    """
    Return a boolean value for whether the given file is tracked by git.
    """
    with chdir(get_root()):
        # https://stackoverflow.com/a/2406813
        result = run_command('git ls-files --error-unmatch {}'.format(filename), capture=True)
        return result.code == 0