Fix crashes with <iframe> tag

[Ryabchikus]

If you have <iframe> tag in your html content htmlparser2 v3.10.1 tries to use Webview from 'react-native' for render it and crash
Minimum example of the content on which the error occurs
const content = "<iframe width="640" height="360" src="https://www.youtube.com/embed/iwKAE3rLGoQ?&wmode=opaque" frameborder="0" allowfullscreen="" class="fr-draggable"></iframe>"

This PR fix crashes.

• update 'htmlparser2' dependency to v4.0.0
• small changes for correct work with new htmlparser2 version
• move 'react-native-webview' dependency to 'peerDependencies' section, because 'react-native-webview' must be linked before using
• add note about 'react-native-webview' dependency to readme.md file

[bd-arc]

Thanks for the PR! Available in version 4.2.0.

[pragneshpj]

iFrame keep crashing in android.
react-native-render-html : 4.2.2

[jsamr]

@pragneshpj Please open a bug report, offer a reproduction, and I'll be happy to investigate and fix this.

[jsamr]

@pragneshpj Actually it might have been fixed in the latest pre-release. See #390 to see how to install it.

[pragneshpj]

@jsamr thank you for responding.
but this beta version also crashing iFrame post.

[jsamr]

@pragneshpj OK, we can figure this out on discord!