flake8 of flux_analysis directory

[akaviaLab]

• description of feature/fix
  Corrected flake8 issues on flux_analysis directory
  Corrected typing a bit

[codecov-commenter]

Codecov Report

Merging #1227 (a51024a) into devel (e838e54) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##            devel    #1227   +/-   ##
=======================================
  Coverage   84.59%   84.59%           
=======================================
  Files          66       66           
  Lines        5491     5491           
  Branches     1264     1264           
=======================================
  Hits         4645     4645           
  Misses        545      545           
  Partials      301      301           

Impacted Files	Coverage Δ
src/cobra/flux_analysis/__init__.py	100.00% <ø> (ø)
src/cobra/flux_analysis/deletion.py	89.47% <100.00%> (ø)
src/cobra/flux_analysis/gapfilling.py	92.70% <100.00%> (ø)
src/cobra/flux_analysis/phenotype_phase_plane.py	83.00% <100.00%> (ø)
src/cobra/flux_analysis/reaction.py	76.36% <100.00%> (ø)

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[Midnighter]

Looks good 👍🏼