Make serve.js generate kaitaiFsFiles like serve.py did.

[jchv]

This fixes an issue caused by #95 where kaitaiFsFiles never gets updated/generated in the root, causing the app to not load in serve mode when it is freshly cloned and no kaitaiFsFiles file exists yet. In the original serve.py implementation, it was generated regardless of whether or not the --compile flag was passed, so I've taken this route as well.

It should be possible to reproduce this issue by simply cloning and running node serve.js --compile.

[generalmimon]

@jchv Thanks for the fix. I actually noticed this change compared to the original script, but then rejected it as a problem, because the build script executes the genKaitaiFsFiles manually.

But I agree that it makes sense to execute it in the development environment along with node serve.js --compile as well, given that the Python script has worked this way.

LGTM, merging in.

[jchv]

@generalmimon It's actually worse: the build script only generates it into the out folder. So afaict, if you clone fresh, you would never get a kaitaiFsFiles.js that would be served by node serve.js, even if you did run build, since serve.js serves from the root. Whether there really needs to be a separate out folder or not is another question. I think I missed this subtlety when I was originally working on this somehow, probably because I was more focused on making sure the out folder was outputting the same thing.