Fix Handling of Workspace Packages

[jtpio]

Ensure each sub-package is a directory and has a package.json file.

[codecov-commenter]

Codecov Report

Merging #53 (409073a) into master (5b17742) will decrease coverage by 0.95%.
The diff coverage is 78.81%.

@@            Coverage Diff             @@
##           master      #53      +/-   ##
==========================================
- Coverage   89.03%   88.08%   -0.96%     
==========================================
  Files          15       15              
  Lines        1697     1746      +49     
  Branches      198      213      +15     
==========================================
+ Hits         1511     1538      +27     
- Misses        118      128      +10     
- Partials       68       80      +12     

Impacted Files	Coverage Δ
jupyter_releaser/tests/test_functions.py	100.00% <ø> (ø)
jupyter_releaser/changelog.py	88.18% <62.50%> (-2.56%)	⬇️
jupyter_releaser/npm.py	78.83% <65.71%> (-4.91%)	⬇️
jupyter_releaser/lib.py	75.29% <70.00%> (-2.46%)	⬇️
jupyter_releaser/tests/test_cli.py	97.64% <91.66%> (-0.20%)	⬇️
jupyter_releaser/__init__.py	100.00% <100.00%> (ø)
jupyter_releaser/cli.py	92.27% <100.00%> (+0.03%)	⬆️
jupyter_releaser/python.py	91.66% <100.00%> (+3.78%)	⬆️
jupyter_releaser/tests/conftest.py	98.50% <100.00%> (+0.01%)	⬆️
jupyter_releaser/util.py	85.00% <100.00%> (+0.10%)	⬆️

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[blink1073]

Thank you!