fix: do not crash if pkg.(d|devD)ependencies unset

[mcous]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

Fixes #547. dependencies and devDependencies are not required fields of package.json, but the existing code assumes they are always present, which can throw an uncaught error.

Breaking Changes

N/A

Additional Info

I no longer use this library, but I got tired of my stale ticket sitting around in my issues list 😜

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: mcous / name: Michael Cousins (e71c85e)
• ✅ login: alexander-akait / name: Alexander Akait (ee0c90f)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (84f16be) 88.70% compared to head (ee0c90f) 88.73%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #667      +/-   ##
==========================================
+ Coverage   88.70%   88.73%   +0.03%     
==========================================
  Files           3        3              
  Lines         354      355       +1     
  Branches      115      116       +1     
==========================================
+ Hits          314      315       +1     
  Misses         37       37              
  Partials        3        3              

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