Several bug fixes and improvements (#945)

* Update Dockerfile for code debugging.

* Format Python code using Black.

* Improve dark theme by defining html classes for the figures, animations and cover images.

* Fix several glossary translation.

* Update a code comment.

* Fix climbing_stairs_backtrack: the pruning should not require the sorted choices list.

* Update the code of array and list traversal.

* Fix a rendering issue of README.md

* Update code of list traversal.

* Fix array_definition.png

* Update README.md

* Fix max_capacity_moving_short_board.png

* Fix array.dart

* Fix array.dart

* Fix array.dart

* Fix array.dart

codes/swift/chapter_array_and_linkedlist/array.swift

@@ -48,12 +48,12 @@ func remove(nums: inout [Int], index: Int) {
 func traverse(nums: [Int]) {
     var count = 0
     // 通过索引遍历数组
-    for _ in nums.indices {
-        count += 1
+    for i in nums.indices {
+        count += nums[i]
     }
-    // 直接遍历数组
-    for _ in nums {
-        count += 1
+    // 直接遍历数组元素
+    for num in nums {
+        count += num
     }
 }