Set permissions on start.sh in Dockerfile

Fixes Haarlem#4 

The `docker-compose up` command failed because it could not execute `/start.sh` failing with the following error:

> ERROR: for web  Cannot start service web: OCI runtime create failed: container_linux.go:348: starting container process caused "exec: \"/start.sh\": permission denied": unknown

Dockerfile

@@ -36,11 +36,12 @@ RUN apk --no-cache add \
 
 COPY ./src /app/src
 COPY ./docker/start.sh /start.sh
+RUN chmod +x /start.sh
 RUN mkdir /app/log
 
 COPY --from=build /app/env /app/env
 
 ENV PATH="/app/env/bin:${PATH}"
 WORKDIR /app
 EXPOSE 8000
-CMD ["/start.sh"]
+CMD ["/start.sh"]