remove stdcxx namespace and use std directly
diff --git a/lib/cpp/src/thrift/concurrency/Monitor.cpp b/lib/cpp/src/thrift/concurrency/Monitor.cpp
index 8e4ac79..9570cc6 100644
--- a/lib/cpp/src/thrift/concurrency/Monitor.cpp
+++ b/lib/cpp/src/thrift/concurrency/Monitor.cpp
@@ -34,7 +34,7 @@
 namespace apache {
 namespace thrift {
 
-using std::scoped_ptr;
+using std::unique_ptr;
 using std::shared_ptr;
 
 namespace concurrency {
@@ -163,7 +163,7 @@
     }
   }
 
-  scoped_ptr<Mutex> ownedMutex_;
+  unique_ptr<Mutex> ownedMutex_;
   Mutex* mutex_;
 
   mutable pthread_cond_t pthread_cond_;