[MRG] BUG: objective function in optimization.py should return a scalar

[rythorpe]

The goal here is to fix a few minor bugs that have popped up in master branch due to updates in dependencies. The biggest one revealed a bug on our end (as the title states), but the others were caused by an update in flake8 and a divergence between the object returned by pytest's legacy tmpdir (py.path.local instance) and what h5py expects to read from / write to (a str specifying a path or pathlib.Path instance).

[codecov-commenter]

Codecov Report

Merging #670 (2be24fd) into master (c81e5b8) will not change coverage. The diff coverage is 100.00%.

:exclamation: Current head 2be24fd differs from pull request most recent head cd4ccef. Consider uploading reports for the commit cd4ccef to get more accurate results

:exclamation: Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

@@           Coverage Diff           @@
##           master     #670   +/-   ##
=======================================
  Coverage   91.55%   91.55%           
=======================================
  Files          22       22           
  Lines        4405     4405           
=======================================
  Hits         4033     4033           
  Misses        372      372           

Files Changed	Coverage Δ
hnn_core/optimization.py	92.99% <100.00%> (ø)

[rythorpe]

@ntolley @raj1701 @jasmainak see if this makes sense and will (hopefully) minimally impact the current PRs that are open. Note that I didn't write a test for the optimization bug since we're in the process of deprecating this routine with #652, but am happy to if any of you think it'd be best.

[jasmainak]

your tests are failing ...

[rythorpe]

Yep, I'm rerunning them now. Something about test_viz.py (which was untouched) failing....

[jasmainak]

Thanks @rythorpe !