app-interact/lecture: Change reference to reader/sender demo

The slides were incorrectly referencing demos in the `demo/send-receive/`
folder, which doesn't exits. This replaces `send-receive` with the correct
folder name: `comm-channels`.

Signed-off-by: Teodor Dutu <teodor.dutu@gmail.com>

Author: teodutu

content/chapters/app-interact/lecture/slides/defs.md

@@ -36,9 +36,9 @@ int main(void)
 
 ### Exhibit 1 - Creating Interaction
 
-- `demo/send-receive/reader.c`
-- `demo/send-receive/writer.c`
-- `demo/send-receive/send_receive_pipe.c`
+- `demo/comm-channels/reader.c`
+- `demo/comm-channels/writer.c`
+- `demo/comm-channels/send_receive_pipe.c`
 
 ---