Add a missing blank line (style nit)

Summary: [Folly] Add a missing blank line (style nit).

Reviewed By: lewissbaker

Differential Revision: D13571222

fbshipit-source-id: 1dd23f4fc895e5698f94be6b2cbf90a9f30aae41

folly/experimental/coro/test/CoroTest.cpp

@@ -437,4 +437,5 @@ TEST(Coro, Semaphore) {
     EXPECT_EQ(0, worker.counter);
   }
 }
+
 #endif