fix style, & add note comment

Author: rixo

runtime/proxy-adapter-dom.js

@@ -1,8 +1,14 @@
 /* global window, document */
 import * as svelteInternal from 'svelte/internal'
+// NOTE from 3.38.3 (or so), insert was carrying the hydration logic, that must
+// be used because DOM elements are reused more (and so insertion points are not
+// necessarily added in order); then in 3.40 the logic was moved to
+// insert_hydration, which is the one we must use for HMR
 const svelteInsert = svelteInternal.insert_hydration || svelteInternal.insert
-if(!svelteInsert) {
-  throw new Error('failed to find insert_hydration and insert in svelte/internal')
+if (!svelteInsert) {
+  throw new Error(
+    'failed to find insert_hydration and insert in svelte/internal'
+  )
 }
 
 import ErrorOverlay from './overlay.js'