v0.6.0-rc.2021022601

• Migrate to null safety (#436, authored by @miDeb)

Deployed 2f191a9 to https://api-mm20lnu18-flutter-widget-from-html.vercel.app.

Quick links:

• iframe

Deployed 2f191a9 to https://example-7esp3rcv0-flutter-widget-from-html.vercel.app.

Quick links:

• supported/tags.html
• Hello World
• Hello World (core)
• Wordpress
• --web-renderer canvaskit
• --web-renderer html