By default this has been removed from WooCommerce 2.6 to avoid obvious situations such as “Free Shipping: (Free)”, but in some cases it’s required display some message and this is possible with the following code.
https://gist.github.com/claudiosanches/93de81025d212fec4e2d8ac86ee101e3
Note that the code above don’t include any message for the “Free Shipping” method.