Fix diagram

Author: acogoluegnes

deps/rabbitmq_stream/docs/stream_coordinator.md

@@ -21,7 +21,7 @@ sequenceDiagram
     deactivate C1
     C-)C2: {sac, sub 2, active = true}
     activate C2
-    C1->>C1: consumer update to client
+    C2->>C2: consumer update to client
     deactivate C2
 ```