remove using std

Change-Id: I268a92200a397f4fba0458f951f0a10b25ac0836
diff --git a/src/name-assignments/assignment-funcs.hpp b/src/name-assignments/assignment-funcs.hpp
index 3f78955..30408b5 100644
--- a/src/name-assignments/assignment-funcs.hpp
+++ b/src/name-assignments/assignment-funcs.hpp
@@ -54,7 +54,7 @@
   {
     FuncFactoryFactory& factory = getFactory();
     BOOST_ASSERT(factory.count(typeName) == 0);
-    factory[typeName] = [](const std::string& format) { return make_unique<ChallengeType>(format); };
+    factory[typeName] = [](const std::string& format) { return std::make_unique<ChallengeType>(format); };
   }
 
   static unique_ptr<NameAssignmentFunc>