matplotlib warnings: norm + vmin, vmax

[lheagy]

update the logic in plotting so that we don't pass both a norm and vmin, vmax to resolve the Matplotlib warning:

MatplotlibDeprecationWarning: Passing parameters norm and vmin/vmax simultaneously is deprecated since 3.3 and will become an error two minor releases later. Please pass vmin/vmax directly to the norm when creating it.

[codecov]

Codecov Report

Merging #226 into master will decrease coverage by 0.05%.
The diff coverage is 64.70%.

@@            Coverage Diff             @@
##           master     #226      +/-   ##
==========================================
- Coverage   82.59%   82.53%   -0.06%     
==========================================
  Files          24       24              
  Lines        5488     5504      +16     
==========================================
+ Hits         4533     4543      +10     
- Misses        955      961       +6     

Impacted Files	Coverage Δ
discretize/View.py	70.84% <64.70%> (-0.15%)	⬇️

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[prisae]

Along the lines of what I mentioned in #227 - I think it is good to mention why something (issue/PR) was closed, e.g., fixed in #xyz, it was decided it will not be fixed, this is outdated due to xyz, etc.

Users often stumble to (open or closed) GitHub issues and PR's, so it is good to guide them to the solution.

This issue was fixed in #227.