Fix Flux deprecations and example files

[sdobber]

Change ADAM to Adam, replace Flux.Zygote.@nograd with Flux.ChainRulesCore.@non_differentiable, and update the examples with

Flux.ChainRulesCore.ignore_derivatives() do
        Flux.reset!(model)
end

to avoid errors coming from differentiating through the reset!-call.