Allow to pass any arguments to z

before:

```
$ z --help
12         /Users/Jean/Dropbox
12         /Users/Jean/work

$ z work
/Users/Jean/work
```

after:

```
z --help
z [-chlrtx] args

$ z work
/Users/Jean/work
```

plugins/z/z.fish

 function z
-  cd (bash -c 'source $Z_SCRIPT_PATH; _z $0; echo $PWD' $argv)
+  cd (bash -c "source $Z_SCRIPT_PATH; _z $argv; echo \$PWD")
 end