fix: fix the bug that threads don't stop when pegasus_io_service is released (#455)

rdsn @ d1cb30c6

-Subproject commit 9679e40fcd86edff5018bad67e8ba2c74412fd44
+Subproject commit d1cb30c6b0a3b9f08cf2501e8f193c7be4e87965

src/reporter/pegasus_io_service.h

@@ -30,6 +30,14 @@ public:
         }
     }
 
+    ~pegasus_io_service()
+    {
+        ios.stop();
+        for (auto worker : _workers) {
+            worker->join();
+        }
+    }
+
     boost::asio::io_service ios;
 
 private: