Complete the Subpage.open() method

src/main/kotlin/fr/username404/website/subpages/Subpage.kt

@@ -12,5 +12,8 @@ data class Subpage(
     val meta: Set<HTMLMetaElement>?,
     val content: HTMLElement
 ) {
-    fun open(): Document = window.document.open(type = "text/html", replace = content.innerHTML)
+    fun open(): Document = window.document.open(
+        type = "text/html",
+        replace = head.map { it.innerHTML }.reduce { previous, current -> previous + "\n" + current }
+    )
 }