Fix demo mode

[atrovato]

Pull Request check-list

To ensure your Pull Request can be accepted as fast as possible, make sure to review and check all of these items:

• [ ] If your changes affects code, did your write the tests?
• [ ] Are tests passing? (npm test on both front/server)
• [ ] Is the linter passing? (npm run eslint on both front/server)
• [ ] Did you run prettier? (npm run prettier on both front/server)
• [ ] If you are adding a new features/services, did you run integration comparator? (npm run compare-translations on front)
• [ ] Did you test this pull request in real life? With real devices? If this development is a big feature or a new service, we recommend that you provide a Docker image to the community for testing before merging.
• [ ] If your changes modify the API (REST or Node.js), did you modify the API documentation? (Documentation is based on comments in code)
• [ ] If you are adding a new features/services which needs explanation, did you modify the user documentation? See the GitHub repo and the website.
• [ ] Did you add fake requests data for the demo mode (front/src/config/demo.js) so that the demo website is working without a backend? (if needed) See https://demo.gladysassistant.com.

NOTE: these things are not required to open a PR and can be done afterwards / while the PR is open.

Description of change

Please provide a description of the change here. It's always best with screenshots, so don't hesitate to add some!

[codecov[bot]]

Codecov Report

Merging #24 (0c13972) into master (c14e042) will decrease coverage by 0.01%. The diff coverage is 98.41%.

:exclamation: Current head 0c13972 differs from pull request most recent head 60046a6. Consider uploading reports for the commit 60046a6 to get more accurate results

@@            Coverage Diff             @@
##           master      #24      +/-   ##
==========================================
- Coverage   96.55%   96.54%   -0.02%     
==========================================
  Files         669      613      -56     
  Lines        8625     8729     +104     
==========================================
+ Hits         8328     8427      +99     
- Misses        297      302       +5     

Impacted Files	Coverage Δ
server/config/scheduler-jobs.js	100.00% <ø> (ø)
server/models/dashboard.js	100.00% <ø> (ø)
server/models/device_feature.js	100.00% <ø> (ø)
server/services/ewelink/lib/features/humidity.js	90.90% <90.90%> (ø)
...erver/services/ewelink/lib/features/temperature.js	90.90% <90.90%> (ø)
server/lib/job/job.updateProgress.js	92.30% <92.30%> (ø)
server/lib/device/device.calculateAggregate.js	94.00% <94.00%> (ø)
server/services/ewelink/lib/device/poll.js	97.82% <96.96%> (-2.18%)	:arrow_down:
...b/device/device.calculcateAggregateChildProcess.js	97.01% <97.01%> (ø)
server/api/controllers/device.controller.js	73.91% <100.00%> (+2.48%)	:arrow_up:
... and 45 more

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