Fix finding JSON feeds with new MIME type
Fix finding JSON feeds with new MIME type

The 1.1 version (https://jsonfeed.org/version/1.1) for JSON feeds defines that feeds should have a MIME type of `application/feed+json` which Miniflux wasn't searching for

xqin/miniflux,miniflux/miniflux,xqin/miniflux,miniflux/miniflux,xqin/miniflux,miniflux/miniflux,xqin/miniflux