char-rnn notebook broken on release versions of Flux, CuArrays

[ViralBShah]

When using CuArrays, char-rnn breaks on train!. Maybe flux-notebooks can have CI too using NBInclude?

Broadcast output type Any is not concrete

Stacktrace:
 [1] broadcast_t at /home/jrun/.julia/v0.6/CuArrays/src/broadcast.jl:34 [inlined]
 [2] broadcast_c at /home/jrun/.julia/v0.6/CuArrays/src/broadcast.jl:63 [inlined]
 [3] broadcast at ./broadcast.jl:455 [inlined]
 [4] tracked_broadcast(::Function, ::Flux.OneHotMatrix{CuArray{Flux.OneHotVector,1}}, ::TrackedArray{…,CuArray{Float32,2}}, ::Int64) at /home/jrun/.julia/v0.6/Flux/src/tracker/array.jl:278
 [5] #crossentropy#71(::Int64, ::Function, ::TrackedArray{…,CuArray{Float32,2}}, ::Flux.OneHotMatrix{CuArray{Flux.OneHotVector,1}}) at /home/jrun/.julia/v0.6/Flux/src/layers/stateless.jl:8
 [6] crossentropy(::TrackedArray{…,CuArray{Float32,2}}, ::Flux.OneHotMatrix{CuArray{Flux.OneHotVector,1}}) at /home/jrun/.julia/v0.6/Flux/src/layers/stateless.jl:8
 [7] (::##3#4)(::Flux.OneHotMatrix{Array{Flux.OneHotVector,1}}, ::Flux.OneHotMatrix{Array{Flux.OneHotVector,1}}) at ./<missing>:0
 [8] broadcast_t(::Function, ::Type{Any}, ::Tuple{Base.OneTo{Int64}}, ::CartesianRange{CartesianIndex{1}}, ::Array{Flux.OneHotMatrix{Array{Flux.OneHotVector,1}},1}, ::Array{Flux.OneHotMatrix{Array{Flux.OneHotVector,1}},1}) at ./broadcast.jl:258
 [9] broadcast_c at ./broadcast.jl:321 [inlined]
 [10] broadcast at ./broadcast.jl:455 [inlined]
 [11] loss(::Array{Flux.OneHotMatrix{Array{Flux.OneHotVector,1}},1}, ::Array{Flux.OneHotMatrix{Array{Flux.OneHotVector,1}},1}) at ./In[4]:12
 [12] macro expansion at /home/jrun/.julia/v0.6/Flux/src/optimise/train.jl:39 [inlined]
 [13] macro expansion at /home/jrun/.julia/v0.6/Juno/src/progress.jl:119 [inlined]
 [14] #train!#130(::Flux.#throttled#14, ::Function, ::Function, ::Base.Iterators.Zip2{Array{Array{Flux.OneHotMatrix{Array{Flux.OneHotVector,1}},1},1},Array{Array{Flux.OneHotMatrix{Array{Flux.OneHotVector,1}},1},1}}, ::Flux.Optimise.##71#75) at /home/jrun/.julia/v0.6/Flux/src/optimise/train.jl:38
 [15] (::Flux.Optimise.#kw##train!)(::Array{Any,1}, ::Flux.Optimise.#train!, ::Function, ::Base.Iterators.Zip2{Array{Array{Flux.OneHotMatrix{Array{Flux.OneHotVector,1}},1},1},Array{Array{Flux.OneHotMatrix{Array{Flux.OneHotVector,1}},1},1}}, ::Function) at ./<missing>:0
 [16] include_string(::String, ::String) at ./loading.jl:522
​```