pyWeMo serialnumber is deprecated, use serial_number

[esev]

Proposed change

Rename serialnumber to serial_number in the wemo component. serialnumber was deprecated in pyWeMo 0.8.0 and will be removed in a future release.

HomeAssistant is currently using pywemo 0.9.1 which supports both serialnumber and serial_number.

core/homeassistant/components/wemo/manifest.json

Line 12 in be638d3

"requirements": ["pywemo==0.9.1"],

serialnumber transitional wrapper: https://github.com/pywemo/pywemo/blob/0.9.1/pywemo/ouimeaux_device/__init__.py#L688

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
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Checklist

• The code change is tested and works locally.
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• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

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• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
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