fix a typo

Author: mcabbott

src/dropout.jl

@@ -63,7 +63,7 @@ dropout!(B::AbstractArray, A::AbstractArray, p::Real; dims = :) = dropout!(_rng_
 function dropout!(rng::AbstractRNG, dst::AbstractArray, src::AbstractArray, p::Real; dims=:)
     size(dst) == size(src) || throw(DimensionMismatch("dropout! expects output array the same size as input"))
     0 <= p <= 1 || throw(ArgumentError("dropout expects a probability 0 <= p <= 1"))
-    _rng_compat_array(rng, A)
+    _rng_compat_array(rng, src)
     if p > 0
         pT = convert(real(eltype(dst)), p)
         _dropout!(rng, dst, src, pT, dims)