Revert is-plain-object dependency changes

[cyamonide]

Description

This PR reverts the dependency changes landed as attempts to fix the is-plain-object bundling problems.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #207 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #207   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          334       334           
  Branches        42        42           
=========================================
  Hits           334       334           

Flag	Coverage Δ
#unittests	100.00% <ø> (ø)

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

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c9897ae...12d4e68. Read the comment docs.