fix quote stripping

[almdudler777]

Hi,

When running from .env file quotes will be correctly stripped in the current version.

But when that same .env file is loaded through a docker-compose.yml
it will internally be loaded through os.environ and not be stripped of quotes.

This commit fixes and synchronizes this behaviour.

[almdudler777]

On second thought, it might be better to apply the stripping only to values casted to non-string types.

Reason:
I'm unsure about what will happen to something like PATH="/some/path/with whitespace" myprogram.py
In an .env file quotes should be optional as the equal (=) sign and the line-break are the separators.
On the cmd-line paths with whitespace in them need to be surrounded by quotes as the whitespace is a reserved character.

[henriquebastos]

Can you provide regression tests to expose the problem and the actual fix?