Switch Problems 31 and 30

[Dhanvanthri]

Here are the solutions that I used for 30 and 31 respectively

30: #(map first (partition-by identity %1)) 31: #(partition-by identity %1)

I know that the exercises are all very freeform, but I do think that each problem has a few highly idiomatic solutions (and for these 2 I think the ones I've provided are idiomatic); Since problem 30 builds off of problem 31, I think their order should be switched.

Thank you so much for the 4clojure project!