refactor(Headings extension): use tag func

src/extensions/headings/index.ts

@@ -1,4 +1,4 @@
-import { create, replace, select, ready, attr } from '../../util'
+import { select, ready, tag } from '../../util'
 
 /**
  * Find all heading nodes and change their depth to depth +1
@@ -11,10 +11,6 @@ ready(() => {
   select(':--Heading').forEach(heading => {
     const level = parseFloat(/^H([1-6])$/.exec(heading.tagName)?.[1] ?? '0')
     const newLevel = Math.min(level + 1, 6)
-    replace(
-      heading,
-      // Using innerHTML seems less than ideal, but given this is only meant to be temporary...
-      create(`h${newLevel} :--Heading`, heading.innerHTML)
-    )
+    tag(heading,`h${newLevel}`)
   })
 })