Move property so it is in the right category

index_on_404 was never used with the default config because the property is set on `web.watcher` and not on `web.app`

src/assets/dioxus.toml

@@ -19,10 +19,10 @@ asset_dir = "public"
 # HTML title tag content
 title = "Dioxus | An elegant GUI library for Rust"
 
-index_on_404 = true
-
 [web.watcher]
 
+index_on_404 = true
+
 watch_path = ["src"]
 
 # include `assets` in web platform