Usually, we have some decent Ruby people respond to this, but since I have not seen any responses yet, I’m going to try to help. Caveat: As you may have guessed, I am not a Ruby expert 
I think the error has less to do with the _ssl issue, and more with the previous error that says unable to load the EventMachine C extension.
Check out this article to see if it is the immediate fix you need:
Also, please carefully review the guidance in the installation documentation I share below. Very often there is a path or environment variable that was not set on the development machine that causes odd errors like this.
If you are still encountering issues, please share what you are typing to get the error. For example, are you typing bundle exec jekyll serve?