Use `randn` in noise for Bayesian example

[codecov[bot]]

Codecov Report

Merging #35 into master will decrease coverage by 0.18%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #35      +/-   ##
==========================================
- Coverage   32.67%   32.48%   -0.19%     
==========================================
  Files          65       65              
  Lines        2286     2287       +1     
==========================================
- Hits          747      743       -4     
- Misses       1539     1544       +5     

Impacted Files	Coverage Δ
src/contexts/hierarchical/simulate.jl	50.00% <0.00%> (-40.91%)	:arrow_down:

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[mschauer]

You probably also want to do

est_β = sum(map(zip(ps.calls, lnw)) do (cl, w)
                 get_ret(cl[:β])*exp(w)
             end) 
println("Estimated β: $est_β") # 2.99...