chore(deps): update dependency html-webpack-plugin to v3 (master)

[appcues-wss]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
html-webpack-plugin	^2.22.0 -> ^3.0.0

By merging this PR, the below vulnerabilities will be automatically resolved:

Severity	CVSS Score	CVE
High	7.5	CVE-2017-16099
Medium	5.3	WS-2019-0017

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Release Notes

jantimon/html-webpack-plugin (html-webpack-plugin)

v3.0.0

Compare Source

Features

• Add support for the new webpack tapable to be compatible with webpack 4.x
• Remove bluebird dependency

BREAKING CHANGES

• Similar to webpack 4.x the support for node versions older than 6 are no longer supported

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