Error thrown when calling `rand(d::GaussianLaguerre, dims::Dim2)` method

While writing docstrings for `rand` methods I found this:
```
julia> rand(GaussianLaguerre(2, 1.0), (3, 3))
ERROR: UndefVarError: `a` not defined in `RandomMatrices`
Suggestion: check for spelling errors or missing imports.
Stacktrace:
[1] rand(d::GaussianLaguerre, dims::Tuple{Int64, Int64})
@ RandomMatrices ~/Documents/Julia Packages/JuliaMatrices/RandomMatrices.jl/src/GaussianEnsembles.jl:180
[2] top-level scope
@ REPL[54]:1
```
Originates from not accessing `a` from the object `d`. Tests should be added for this method too as it looks a little suspicious as is:
https://github.com/JuliaMath/RandomMatrices.jl/blob/c76044d43e718900e72fe71266955c65a47258b0/src/GaussianEnsembles.jl#L149-L173