pushing fix for environment.yml

[jGaboardi]

• Python 3.8 doesn't appear to be playing nicely within the binder environment, so bumping back down to 3.7 for now
• Also adding matplotlib_scalebar to environment.yml.

[codecov]

Codecov Report

Merging #423 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #423   +/-   ##
=======================================
  Coverage   98.07%   98.07%           
=======================================
  Files           5        5           
  Lines        1770     1770           
  Branches      220      220           
=======================================
  Hits         1736     1736           
  Misses         14       14           
  Partials       20       20

Impacted Files	Coverage Δ
spaghetti/util.py	98.95% <0%> (ø)	⬆️
spaghetti/tests/test_network_api.py	100% <0%> (ø)	⬆️
spaghetti/tests/test_network.py	100% <0%> (ø)	⬆️
spaghetti/network.py	95.39% <0%> (ø)	⬆️

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