Fix deprecation of Product

[devmotion]

Fixes #1589.

With this PR (and julia --depwarn=yes):

julia> product_distribution(fill(Weibull(), 5))
Product{Continuous, Weibull{Float64}, Vector{Weibull{Float64}}}(v=Weibull{Float64}[Weibull{Float64}(α=1.0, θ=1.0), Weibull{Float64}(α=1.0, θ=1.0), Weibull{Float64}(α=1.0, θ=1.0), Weibull{Float64}(α=1.0, θ=1.0), Weibull{Float64}(α=1.0, θ=1.0)])

julia> Product(fill(Weibull(), 5))
┌ Warning: Product(v) is deprecated, please use product_distribution(v)
│   caller = top-level scope at REPL[5]:1
└ @ Core REPL[5]:1
Product{Continuous, Weibull{Float64}, Vector{Weibull{Float64}}}(v=Weibull{Float64}[Weibull{Float64}(α=1.0, θ=1.0), Weibull{Float64}(α=1.0, θ=1.0), Weibull{Float64}(α=1.0, θ=1.0), Weibull{Float64}(α=1.0, θ=1.0), Weibull{Float64}(α=1.0, θ=1.0)])

[codecov-commenter]

Codecov Report

Merging #1590 (4a045be) into master (c664d78) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1590   +/-   ##
=======================================
  Coverage   85.73%   85.74%           
=======================================
  Files         129      129           
  Lines        7971     7975    +4     
=======================================
+ Hits         6834     6838    +4     
  Misses       1137     1137           

Impacted Files	Coverage Δ
src/multivariate/product.jl	100.00% <100.00%> (ø)
src/product.jl	100.00% <100.00%> (ø)

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[oschulz]

Thanks!