The tutorial is copyright by Sam Aaron unless a specific author is stated with the comment # coded by ... in which case the copyright is associated with that author (2015) and the content is released under the CC BY-SA 4.0 license:
http://creativecommons.org/licenses/by-sa/4.0/
The original licsense disclaimer can be found here:
https://github.com/sonic-pi-net/sonic-pi/blob/dev/LICENSE.md