cap Zygote version for now

workaround for FluxML/Zygote.jl#547 (comment)

Author: marius311

Project.toml

@@ -75,5 +75,5 @@ Setfield = "0.6.0"
 StaticArrays = "0.12.1"
 StatsBase = "0.32.0"
 Strided = "0.3.3"
-Zygote = "0.4.14"
+Zygote = "0.4.14 - 0.4.15"
 julia = "1.3"