Fix no jump when query begins with - in Zsh

Without this commit, the following command prints the
path found by autojump, but doesn't actually jump because
the Zsh script assumes we're passing an option to j():

    j -- -tools

The -- is needed; otherwise `-tools` would be interpreted as
a (bad) autojump option.

The Bash version (and probably others) does the same, but
this commit only fixes it for Zsh.