lock_guard: remove explicit template

Change-Id: Iec6d57d6a66557a66096c7a8f67e025c6ca5a64c
diff --git a/tools/dnc/dnc.cpp b/tools/dnc/dnc.cpp
index 6bde30e..3923716 100644
--- a/tools/dnc/dnc.cpp
+++ b/tools/dnc/dnc.cpp
@@ -99,7 +99,7 @@
     });
 
     std::mutex mtx;
-    std::unique_lock<std::mutex> lk {mtx};
+    std::unique_lock lk {mtx};
 
     connectionManager->onChannelRequest(
         [&](const std::shared_ptr<dht::crypto::Certificate>&, const std::string& name) {