allow Functor 0.5 (#186)

Author: CarloLucibello

Project.toml

@@ -12,7 +12,7 @@ Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 
 [compat]
 ChainRulesCore = "1"
-Functors = "0.4.9"
+Functors = "0.4.9, 0.5"
 Statistics = "1"
 Zygote = "0.6.40"
 julia = "1.6"