Get rid of push_back in favor of emplace_back

Change-Id: I4a0096441ed725eb21e42eb9cc17a173929e3788
diff --git a/src/ast_path.cpp b/src/ast_path.cpp
index 0d8a606..8a41279 100644
--- a/src/ast_path.cpp
+++ b/src/ast_path.cpp
@@ -336,7 +336,7 @@
             where.pop_back();
         }
     } else {
-        where.push_back(what);
+        where.emplace_back(what);
     }
 }
 }