Fix: Lock down rand_chacha dependency version t0 0.3.1

Locking down rand_chacha to highest working version, in order to make
this crate buildable.

Version of dependency rand_chacha was unfortunately not locked down
properly in Cargo.toml, in earler development. Was just "0". New version
of rand_chacha was released with API-breaking changes, which broke
monkey_test.

Author: jockbert

Cargo.toml

@@ -18,7 +18,7 @@ maintenance = { status = "actively-developed" }
 [dependencies]
 num-traits = "0.2"
 rand = "0.8.5"
-rand_chacha = "0"
+rand_chacha = "0.3.1"
 panic-message = "0.3.0"
 
 [dev-dependencies]