Update Dockerfile to support v8.1.0 of RMLMapper

```dockerfile
FROM node:20-alpine3.22

RUN apk --no-cache add openjdk21-jre-headless

ADD . /rmlmapper-webapi-js/

WORKDIR rmlmapper-webapi-js
RUN npm install && \
    wget --output-document=rmlmapper.jar https://github.com/RMLio/rmlmapper-java/releases/download/v8.1.0/rmlmapper-8.1.0-r380-all.jar && \
    echo 'v8.1.0' > rmlmapper-version.txt


#after boot
ENTRYPOINT ["./bin/cli.js"]
```