Remove extra semi colon from folly/experimental/coro/Merge-inl.h

Summary:
`-Wextra-semi` or `-Wextra-semi-stmt`

If the code compiles, this is safe to land.

Reviewed By: Orvid

Differential Revision: D57975880

fbshipit-source-id: 2d60cb964fc917722e735c1afce1412f0f4c4458

folly/coro/Merge-inl.h

@@ -267,7 +267,7 @@ AsyncGenerator<Reference, Value> merge(
               detail::callback_record_error, std::move(ex)};
           state_->recordPublished.post();
         }
-      };
+      }
     };
 
     detail::Barrier barrier{1};