The issue is that current Discourse source code requires Ruby version 2.3, while as per screenshot you have Ruby version 2.2.3 installed.
The Mac install script was updated two weeks ago to install Ruby version 2.3, so it seems you will need to run that script again or update Ruby version manually.
Also, can you please paste contents from your console here instead of pasting screenshots? This will help with better indexing on Google search.