Fix E0401 (import error) in demo.py (pylint)

[rzbrk]

See:

• https://github.com/rzbrk/PyVoiceRecognitionV3/actions/runs/3031955069/jobs/4879171135#step:5:118
• https://github.com/rzbrk/PyVoiceRecognitionV3/blob/09ab010960f74802ecae1eff3eb9f952b8486b92/scripts/demo.py#L2

scripts/demo.py:2:0: E0401: Unable to import 'serial' (import-error) scripts/demo.py:2:0: C0411: third party import "from serial import Serial" should be placed before "from PyVoiceRecognitionV3 import PyVoiceRecognitionV3" (wrong-import-order)