Fix PHP missing var warning.

[tareiking]

$taxonomy->slug does not exist in this context, however $taxonomy->query_var does, lets use that instead.

[felixarntz]

Thanks @tareiking! Let's use $taxonomy_slug instead which is defined at this point and produces the result that $taxonomy->slug originally would have.

[tareiking]

Good suggestion, updated PR.

[felixarntz]

I think in line 124 you confused the two variable names, the first one ("name" attribute) should remain $taxonomy->query_var while the ID must be $taxonomy_slug.

[tareiking]

@felixarntz good catch! Updated.