manifest.json extension change

Do you want to request a feature or report a bug? A very nitpicky Feature

What is the current behaviour? preact-cli and its given templates seem to favour manifest.json over manifest.webmanifest. And it works great!

If the current behaviour is a bug, please provide the steps to reproduce. N/A

What is the expected behaviour? manifest.json to use the webmanifest extension (manifest.webmanifest)

If this is a feature request, what is motivation or use case for changing the behaviour? The W3 spec somewhat recently confirmed that they favour the webmanifest extension for app manifests

Please mention other relevant information. N/A