Bug mass errors

[jmccreight]

• User visible changes (including notable bug fixes) are documented in whats-new.rst via update docs for release #257

[codecov-commenter]

Codecov Report

Merging #236 (40fb38a) into develop (2f57332) will decrease coverage by 0.34%.
The diff coverage is 93.20%.

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@@             Coverage Diff             @@
##           develop     #236      +/-   ##
===========================================
- Coverage    79.52%   79.19%   -0.34%     
===========================================
  Files           51       51              
  Lines         6506     6536      +30     
===========================================
+ Hits          5174     5176       +2     
- Misses        1332     1360      +28     

Files	Coverage Δ
pywatershed/base/budget.py	89.17% <100.00%> (+0.25%)	⬆️
pywatershed/base/control.py	92.80% <100.00%> (ø)
pywatershed/hydrology/prms_runoff.py	82.59% <100.00%> (+0.24%)	⬆️
pywatershed/utils/csv_utils.py	86.09% <100.00%> (+0.18%)	⬆️
pywatershed/utils/time_utils.py	86.95% <88.88%> (-2.52%)	⬇️
pywatershed/hydrology/prms_snow.py	90.60% <94.54%> (+0.13%)	⬆️
pywatershed/utils/prms5util.py	31.74% <0.00%> (-0.34%)	⬇️

... and 2 files with indirect coverage changes

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