Branching webpack versions

[echolimazulu]

Hello @developit and other contributors,

There is currently a dependency on "html-webpack-plugin": "^4.5.2". Version 4.5.2 is used with webpack version 4. It may make sense to branch along the same lines as implemented in html-webpack-plugin with the plugin version specified via @: for webpack5 - critters-webpack-plugin for webpack4 - critters-webpack-plugin@4

https://github.com/GoogleChromeLabs/critters/blob/a590c05f9197b656d2aeaae9369df2483c26b072/packages/critters-webpack-plugin/package.json#L63

On webpack version 5, I didn't notice any major compatibility issues.