Make V3 the new master version of this plugin

[AnujRNair]

Summary

This PR will promote the beta version of this plugin to become the new master version of the plugin. Breaking changes from this plugin can be seen in the previous pre-releases here: https://github.com/slackhq/csp-html-webpack-plugin/releases/tag/v3.0.0-beta.1 https://github.com/slackhq/csp-html-webpack-plugin/releases/tag/v3.0.0-beta.2

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 #31 into master will increase coverage by 0.29%. The diff coverage is 96.29%.

@@            Coverage Diff            @@
##           master     #31      +/-   ##
=========================================
+ Coverage    93.5%   93.8%   +0.29%     
=========================================
  Files           2       2              
  Lines          77     113      +36     
  Branches       11      21      +10     
=========================================
+ Hits           72     106      +34     
- Misses          4       6       +2     
  Partials        1       1

Impacted Files	Coverage Δ
test-utils/webpack-helpers.js	100% <100%> (ø)	:arrow_up:
plugin.js	92.3% <95.91%> (+1.23%)	:arrow_up:

---

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 6da3843...c1e9fee. Read the comment docs.