Let me copy the reply I gave on the issue on Github regarding this for whoever isn't following Github issues:
That's a good catch!
We changed `referer` to simply use `Plack::Request`'s `referer` method. This makes it more consistent with another publicly-known interface to a Plack request (the canonical one, in fact).
I'm sorry to hear you had code depending on it which now failed.
Here is the relevant commit:
738b4f15ea3ae72900c17763044cd1ac143d13b3
There was a small mistake there that was fixed in the commit after:
3f885d0d8ca173e5620354be1d5a12802930add7
S.