Ok falola… i solved the problem locally… but i cannot give you a build because the plugin building on 4.18 is broken
https://answers.unrealengine.com/questions/717438/rocket-build-expects-h-to-be-first-include-but-bui.html
I can however, tell you which files to modify to get it working for the time being, so you can compile them on your machine.
I also wouldn’t recommend using 4.18 preview for serious work ATM
Cheers