Simplify FluxApproximator's optimise! method by using a single-line f…

…unction definition

src/ReinforcementLearningCore/src/policies/learners/flux_approximator.jl

@@ -43,8 +43,5 @@ Flux.@layer FluxApproximator trainable=(model,)
 forward(A::FluxApproximator, args...; kwargs...) = A.model(args...; kwargs...)
 forward(A::FluxApproximator, env::E, player::AbstractPlayer=current_player(env)) where {E <: AbstractEnv} = env |> (x -> state(x, player)) |> (x -> forward(A, x))
 
-function RLBase.optimise!(A::FluxApproximator, grad::NamedTuple)
-
-    Flux.Optimise.update!(A.optimiser_state, A.model, grad.model)
-end
+RLBase.optimise!(A::FluxApproximator, grad::NamedTuple) = Flux.Optimise.update!(A.optimiser_state, A.model, grad.model)