Update docs as discussed in #22014 (#22206)

As [discussed](#22014 (comment)) in #22014, the docs are updated to point to a specific revision for the `audacity.rb` example.

doc/cask_language_reference/stanzas/url.md

@@ -123,7 +123,7 @@ The block will be called immediately before downloading; its result value will b
 
 You can use the `url` stanza with either a direct argument or a block but not with both.
 
-Example for using the block syntax: [audacity.rb](https://github.com/caskroom/homebrew-cask/tree/master/Casks/audacity.rb)
+Example for using the block syntax: [audacity.rb](https://github.com/caskroom/homebrew-cask/blob/c389d9ccbb46d30b6ac1cbdbadf49591ca8ff6cd/Casks/audacity.rb#L5-L15)
 
 ### Mixing Additional URL Parameters With the Block Syntax