Fix typo in variable name

[marcpaterno]

This will fix issue #452.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.5%. Comparing base (417c94c) to head (5626c7a).
Report is 18 commits behind head on master.

Additional details and impacted files

@@          Coverage Diff           @@
##           master    #453   +/-   ##
======================================
  Coverage    98.5%   98.5%           
======================================
  Files          50      50           
  Lines        3657    3657           
======================================
  Hits         3604    3604           
  Misses         53      53           

Files with missing lines	Coverage Δ
firecrown/generators/inferred_galaxy_zdist.py	100.0% <100.0%> (ø)