Upgrade more dev deps and peer dep requirements

[AnujRNair]

Summary

Upgrading dev and peer dependencies.

• webpack 5 is now used when testing this plugin
• html-webpack-plugin 5 is now used when testing this plugin
• Updating the peer dependency requirements to ensure only webpack 4 & 5, and only html-webpack-plugin 4 & 5 are supported.

Requirements (place an x in each [ ])

• [x] I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• [x] I've read and agree to the Code of Conduct.
• [x] I've written tests to cover the new code and functionality included in this PR.
• [x] I've read, agree to, and signed the Contributor License Agreement (CLA).

[codecov[bot]]

Codecov Report

Merging #72 (4b2088c) into master (ece9c91) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #72   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines          111       108    -3     
  Branches        21        18    -3     
=========================================
- Hits           111       108    -3     

Impacted Files	Coverage Δ
plugin.js	100.00% <100.00%> (ø)

---

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 ece9c91...4b2088c. Read the comment docs.