use cache_dir instead of output_dir

[montesmariana]

Types of changes

• Bug fix (non-breaking change which fixes an issue), fixing Issue create_dotfile fail if workflow has a splitter #442

Summary

Add the option of specifying the output directory for the dotfile (the graph of a workflow) and when it is not specified, use cache_dir instead of output_dir (because when there is splitting the output_dir attribute is a list of paths instead of a path).

Checklist

I have not added tests or updated documentation (there is no much original documentation on this method that I could find)

[codecov]

Codecov Report

Merging #538 (2e04ffc) into master (726d242) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #538   +/-   ##
=======================================
  Coverage   76.98%   76.98%           
=======================================
  Files          20       20           
  Lines        4279     4280    +1     
  Branches     1204     1204           
=======================================
+ Hits         3294     3295    +1     
  Misses        799      799           
  Partials      186      186           

Flag	Coverage Δ
unittests	76.89% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pydra/engine/core.py	88.95% <100.00%> (+0.01%)	⬆️

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[djarecka]

@montesmariana - I'm sorry, I completely missed this PR... Thank you so much for fixing it!

I will merge it, but could you please add your name to the zenodo file. We haven't kept any particular order, but please just keep Satra Ghosh as the last author.