Dropout with dims test passing.

src/layers/normalise.jl

@@ -14,9 +14,10 @@ Does nothing to the input once in [`testmode!`](@ref).
 """
 mutable struct Dropout{F}
   p::F
-  function Dropout(p)
+  dims::Union{Colon, Int, NTuple{N, Int} where N}
+  function Dropout(p; dims = :)
     @assert 0 ≤ p ≤ 1
-    new{typeof(p)}(p)
+    Dropout{typeof(p)}(p, dims)
   end
 end