update project music

[bjornregnell]

• change sbt to scala-cli in Task 9
• consider removing tip on jline
• make task to implement def mandatory
• invent some more fun optional tasks

[bjornregnell]

fixed by 5d8d492d5bed2353421ac8bc01da77984ec671c2 73c6fa0c8ff6609642ae4920f1e5daf1f4319b1a