mean(x::VectorOfArrays, dims=i) off by factor of size(x,1)

```
julia> using RecursiveArrayTools
julia> using Statistics
julia> x = VectorOfArray([[i+j for i=j:j+2] for j=1:2])
2-element Array{Array{Int64,1},1}:
 [2, 3, 4]
 [4, 5, 6]

julia> mean(x,dims=1), mean(Array(x),dims=1)
([9.0 15.0], [3.0 5.0])

julia> mean(x,dims=2), mean(Array(x),dims=2)
([9.0; 12.0; 15.0], [3.0; 4.0; 5.0])
```