Support "Node" as "Engine" value in examples/pxscene2d/src/about.js

[jmgasper]

The client requested that we implement a new "Engine" value in about.js that lists the JS engine used. This currently works for duktape, and as we add back in the compile-time support for Node, we need to ensure that this Engine field lists either "duktape" or "node", depending on the engine used in the app.