The prerequisite course starts in about 2 weeks [1], so you can still take it if you want before Principles of Reactive Programming starts, you'll be able to see what parts you feel you can skip and which ones are useful. There are other quick introductions to Scala you can take [2],[3],[4] to get a feeling of it.

[1] https://www.coursera.org/course/progfun

[2] http://www.scala-tour.com

[3] http://scalatutorials.com/tour

[4] http://learnxinyminutes.com/docs/scala