Get rid of push_back in favor of emplace_back

Change-Id: I4a0096441ed725eb21e42eb9cc17a173929e3788
diff --git a/src/yang_access.cpp b/src/yang_access.cpp
index d5c0ade..79d1c08 100644
--- a/src/yang_access.cpp
+++ b/src/yang_access.cpp
@@ -260,7 +260,7 @@
                 }
             }
         }
-        res.push_back(instance);
+        res.emplace_back(instance);
     }
     return res;
 }