chat: fix duplicate spec point

Author: AndyTWF

src/chat-features.md

@@ -985,7 +985,7 @@ property inside the `Messages` obejct. From the `Room` level:
   - `(CHA-MR11a)` `[Testable]` The \`delete\` method accepts a message
     (or message serial) as the first parameter to identify which message
     to delete the reaction from.
-    - `(CHA-MR4a1)` `[Testable]` If the `serial` passed to this method
+    - `(CHA-MR11a1)` `[Testable]` If the `serial` passed to this method
       is invalid: `undefined, null, empty string`, an error with code
       40000 must be thrown.
   - `(CHA-MR11b)` `[Testable]` The \`delete\` method accepts a