refactor: use correct type for BroadcastOptions#except

The 'except' attribute is a set of room IDs, which is then converted to
a set of socket IDs in the computeExceptSids() method.

That wasn't caught because both types are aliases for 'string', but
Room could be extended to all primitive values in the future.

Reference: https://developer.mozilla.org/en-US/docs/Glossary/Primitive

Related: https://github.com/socketio/socket.io-adapter/issues/82

lib/index.ts

@@ -16,7 +16,7 @@ export interface BroadcastFlags {
 
 export interface BroadcastOptions {
   rooms: Set<Room>;
-  except?: Set<SocketId>;
+  except?: Set<Room>;
   flags?: BroadcastFlags;
 }