lock_guard: remove explicit template

Change-Id: Iec6d57d6a66557a66096c7a8f67e025c6ca5a64c
diff --git a/tools/benchmark/main.cpp b/tools/benchmark/main.cpp
index 068d133..6823307 100644
--- a/tools/benchmark/main.cpp
+++ b/tools/benchmark/main.cpp
@@ -90,7 +90,7 @@
 {
     BenchResult ret;
     std::mutex mtx;
-    std::unique_lock<std::mutex> lock {mtx};
+    std::unique_lock lock {mtx};
     std::condition_variable serverConVar;
 
     auto boostrap_node = std::make_shared<dht::DhtRunner>();