Fix update-path to work with virtualenv>=20.26.6

[ATRAN2]

Fix for this issue #31
Virtualenv 20.26.6 is no longer writing the VIRTUAL_ENV variable with any kind of quotation marks so we need to loosen our checks to include that
Without the quotation marks, newlines get included in the variable, so we'll need to also include a .strip()

[asottile]

this line makes no sense now (and is broken if the path contained an =)

its intent is to strip quotes so that should not be happening in the unquoted version

[asottile]

specifically: the code that writes this uses shlex.quote -- this should probably use shlex.split to parse this -- something like

value, = shlex.split(line.removeprefix('VIRTUAL_ENV='))

[ATRAN2]

Oh yeah that definitely does work much better, thanks!
Switched to using shlex though I did have to use a split instead of removeprefix since that's not available yet in Python3.8

[Typpexs]

Hey @ATRAN2, you are missing to change the regex of activation path:

activation_path_re = re.compile(                                                          
    r'^(?:set -gx |setenv |)VIRTUAL_ENV[ =][\'"](.*?)[\'"]\s*$',                           
)

is becoming :

_activation_path_re = re.compile(
    r'^(?:set -gx |setenv |)VIRTUAL_ENV[ =][\'"]?(.*?)[\'"]?\s*$',
) 

This one can accept VIRTUAL_ENV with quotes as optionnal