Adds extra normalization to make np.random.choice happy

[nquesada]

Add extra normalization of binary probabilities so that numpy choice gets exactly what it wants. Relevant for this

https://github.com/XanaduAI/photonics/pull/43#issuecomment-906603908

[josh146]

Thanks for getting this so quickly @nquesada!

Do you want to add this to the changelog, and then we can do a very small bugfix release?

[codecov]

Codecov Report

Merging #278 (6c4c3ed) into master (1542332) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #278   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           21        21           
  Lines         1439      1441    +2     
=========================================
+ Hits          1439      1441    +2     

Impacted Files	Coverage Δ
thewalrus/samples.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1542332...6c4c3ed. Read the comment docs.