What is the correct support for parameters of Chisq?

`Distributions.jl` allows to create, e.g. `Chisq(0.5)`, but in this case it cannot be converted to an exponential family member:
```julia
julia> convert(ExponentialFamilyDistribution, Chisq(0.5) )
ERROR: Parameter vector [-0.75] is not a valid natural parameter for distribution Chisq.
```