use emplace where appropriate per clang-tidy

The clang-tidy warning 'modernize-use-emplace' correctly flags a
few places where emplace should be used over push.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I6ca79285a87d6927e718345dc8dce0387e6b1eda
diff --git a/redfish-core/lib/message_registries.hpp b/redfish-core/lib/message_registries.hpp
index 907f6cf..ce147a8 100644
--- a/redfish-core/lib/message_registries.hpp
+++ b/redfish-core/lib/message_registries.hpp
@@ -120,7 +120,7 @@
     asyncResp->res.jsonValue["Id"] = header->registryPrefix;
     asyncResp->res.jsonValue["Registry"] = header->id;
     nlohmann::json::array_t languages;
-    languages.push_back("en");
+    languages.emplace_back("en");
     asyncResp->res.jsonValue["Languages@odata.count"] = languages.size();
     asyncResp->res.jsonValue["Languages"] = std::move(languages);
     nlohmann::json::array_t locationMembers;