docs: update cdn

Author: QingWei-Li

Diff for: docs/cdn.md

@@ -44,4 +44,7 @@ Alternatively, use [compressed files](#compressed-files).
 
 ## Other CDN
 
-[jsDelivr](http://www.jsdelivr.com/projects/docsify) is available.
+- http://www.bootcdn.cn/docsify
+- http://www.jsdelivr.com/projects/docsify
+- https://cdnjs.com/libraries/docsify
+

Diff for: docs/de-de/cdn.md

@@ -44,4 +44,6 @@ Alternativ kannst du auch die [komprimierten Dateien](#komprimierte-dateien) ver
 
 ## Andere CDN
 
-[jsDelivr](http://www.jsdelivr.com/projects/docsify) ist auch verfügbar.
+- http://www.bootcdn.cn/docsify
+- http://www.jsdelivr.com/projects/docsify
+- https://cdnjs.com/libraries/docsify

Diff for: docs/zh-cn/cdn.md

@@ -44,5 +44,6 @@ JS 的压缩文件是原有文件路径的基础上加 `.min`后缀
 
 ## 其他 CDN
 
-[jsDelivr](http://www.jsdelivr.com/projects/docsify) 也是可用的，具体用法参考其文档。
-
+- http://www.bootcdn.cn/docsify
+- http://www.jsdelivr.com/projects/docsify
+- https://cdnjs.com/libraries/docsify