Update poetry.zsh

[mathieulallier807]

No description provided.

[noymer]

Or update README to default: -1

[mattmess1221]

:- is special in bash/zsh variable expansion, so the current code works fine. If you omit, the -, your results may vary.

Using numeric character will make an empty string. Using a alphabetic character will cause a syntax error (zsh: unrecognized modifier).

If you use := instead of :-, it will actually set the variable if it isn't set already.