Upgrading deps to their latest versions

[AnujRNair]

Summary

Upgrading deps to their latest versions. Fixes issue https://github.com/slackhq/csp-html-webpack-plugin/issues/70

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 #71 (981cf2c) into master (dc67c37) will increase coverage by 100.00%. The diff coverage is n/a.

@@              Coverage Diff              @@
##           master       #71        +/-   ##
=============================================
+ Coverage        0   100.00%   +100.00%     
=============================================
  Files           0         2         +2     
  Lines           0       111       +111     
  Branches        0        21        +21     
=============================================
+ Hits            0       111       +111     

Impacted Files	Coverage Δ
test-utils/webpack-helpers.js	100.00% <0.00%> (ø)
plugin.js	100.00% <0.00%> (ø)

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