No, I haven’t read the first one. This is my first Elixir book! 
There are some new language features and some types were deprecated because of the move to Erlang 18. (See the changes between versions on their blog: 1.1 and 1.2). The PragProg page for the book says:
This edition of the book has been updated to cover Elixir 1.2, including the new
withexpression, the exrm release manager, and the removal of deprecated types.
I would think you can find that information on elixir-lang.org or pragdave.me or other blogs on the internet. You maybe can get a discount from having the first edition though.
