Update stateless.jl

src/layers/stateless.jl

@@ -46,6 +46,7 @@ given the prediction `ŷ` and true values `y`.
     Huber loss = |
                  |  δ * (|ŷ - y| - 0.5 * δ), otherwise
 """
+#TODO: remove dropgrad when Zygote can handle this function with CuArrays
 function huber_loss(ŷ, y;  δ=eltype(ŷ)(1))
    abs_error = abs.(ŷ .- y)
    temp = Zygote.dropgrad(abs_error .<  δ)