Many bug fixes and improvements (#1270)

* Add Ruby and Kotlin icons
Add the avatar of @curtishd

* Update README

* Synchronize zh-hant and zh versions.

* Translate the pythontutor blocks to traditional Chinese

* Fix en/mkdocs.yml

* Update the landing page of the en version.

* Fix the Dockerfile

* Refine the en landingpage

* Fix en landing page

* Reset the README.md

zh-hant/codes/kotlin/chapter_tree/binary_tree_bfs.kt

@@ -16,13 +16,14 @@ fun levelOrder(root: TreeNode?): MutableList<Int> {
     val queue = LinkedList<TreeNode?>()
     queue.add(root)
     // 初始化一個串列，用於儲存走訪序列
-    val list = ArrayList<Int>()
-    while (!queue.isEmpty()) {
-        val node = queue.poll() // 隊列出隊
-        list.add(node?.value!!) // 儲存節點值
-        if (node.left != null) queue.offer(node.left) // 左子節點入列
-
-        if (node.right != null) queue.offer(node.right) // 右子節點入列
+    val list = mutableListOf<Int>()
+    while (queue.isNotEmpty()) {
+        val node = queue.poll()      // 隊列出隊
+        list.add(node?._val!!)      // 儲存節點值
+        if (node.left != null)
+            queue.offer(node.left)   // 左子節點入列
+        if (node.right != null)
+            queue.offer(node.right)  // 右子節點入列
     }
     return list
 }