Update link for `Rack socket hijacking API`

- Use valid `fragment identifier` in the URL
- Use `https`

actioncable/README.md

@@ -425,7 +425,7 @@ The above will start a cable server on port 28080.
 
 ### In app
 
-If you are using a server that supports the [Rack socket hijacking API](http://www.rubydoc.info/github/rack/rack/file/SPEC#Hijacking), Action Cable can run alongside your Rails application. For example, to listen for WebSocket requests on `/websocket`, specify that path to `config.action_cable.mount_path`:
+If you are using a server that supports the [Rack socket hijacking API](https://www.rubydoc.info/github/rack/rack/file/SPEC#label-Hijacking), Action Cable can run alongside your Rails application. For example, to listen for WebSocket requests on `/websocket`, specify that path to `config.action_cable.mount_path`:
 
 ```ruby
 # config/application.rb
@@ -459,7 +459,7 @@ support, which means you can use all your regular Rails models with no problems
 as long as you haven't committed any thread-safety sins.
 
 The Action Cable server does _not_ need to be a multi-threaded application server.
-This is because Action Cable uses the [Rack socket hijacking API](http://www.rubydoc.info/github/rack/rack/file/SPEC#Hijacking)
+This is because Action Cable uses the [Rack socket hijacking API](https://www.rubydoc.info/github/rack/rack/file/SPEC#label-Hijacking)
 to take over control of connections from the application server. Action Cable
 then manages connections internally, in a multithreaded manner, regardless of
 whether the application server is multi-threaded or not. So Action Cable works