Update virtual env with requirements packages.

def update():
    """Update virtual env with requirements packages."""
    with settings(warn_only=True):
        print(cyan('\nInstalling/Updating required packages...'))

        pip = local('venv/bin/pip install -U --allow-all-external --src libs -r requirements.txt', capture=True)
        if pip.failed:
            print(red(pip))
            abort("pip exited with return code %i" % pip.return_code)

        print(green('Packages requirements updated.'))