docs: remove BootCDN link from CDN documentation (#2831)

Author: sy-records

docs/cdn.md

@@ -10,7 +10,6 @@ Other CDNs are available and may be required in locations where jsDelivr is not
 
 - https://cdnjs.com/libraries/docsify
 - https://unpkg.com/browse/docsify/
-- https://www.bootcdn.cn/docsify/
 
 ## Specifying versions