When creating a new docker image for the preview server, the TypeScript source
code in `scripts-js/` is not copied over. Instead only the generated JavaScript
core in `scripts-js/dist/` are. Because of that, it is necessary to have run
`yarn build` before running `docker build`, so that the new docker image
contains the latest changes in `scripts-js/`.
This was previously part of the `create-image.sh` script, but was accidentally
removed in 21d213dfc.
Georgios Kalpakas