swh-graphql/Dockerfile: Use proper ENV instruction

apps/swh-graphql/Dockerfile

@@ -16,10 +16,10 @@ COPY --chmod=0755 entrypoint.sh ${workdir}
 
 USER ${user}
 ENV SWH_CONFIG_FILENAME=${configdir}/config.yml
-ENV PORT 5013
+ENV PORT=5013
 EXPOSE $PORT
-ENV THREADS 4
-ENV WORKERS 2
-ENV TIMEOUT 3600
+ENV THREADS=4
+ENV WORKERS=2
+ENV TIMEOUT=3600
 
 ENTRYPOINT [ "/opt/swh/entrypoint.sh" ]