setup.py: support pip >= 10

[FeKn]

DoorPi is not installable from GitHub on Raspbian Stretch because the version of pip.

see also:
https://stackoverflow.com/a/49867265

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The inspection completed: ****

[motom001]

Thank you for your request.

Is it a good practice to use the internal pip functions (like '._internal')?
Maybe we should use another solution like this:
https://stackoverflow.com/a/49837302/10651549

What do you think?