don't modify Location if has no host

e.g. "users.php?update=add&id=16" in wordpress

Author: jjb

lib/rack_reverse_proxy/roundtrip.rb

@@ -179,7 +179,7 @@ def response_location
     end
 
     def need_replace_location?
-      response_headers["Location"] && options[:replace_response_host]
+      response_headers["Location"] && options[:replace_response_host] && response_location.host
     end
 
     def setup_request

spec/rack/reverse_proxy_spec.rb

@@ -354,6 +354,14 @@ def app
         get "https://example.com/test/stuff"
         expect(last_response.headers["location"]).to eq("https://example.com/bar")
       end
+
+      it "doesn't replaces the location response header if it has no host" do
+        stub_request(:get, "http://example.com/test/stuff").to_return(
+          :headers => { "location" => "/bar" }
+        )
+        get "http://example.com/test/stuff"
+        expect(last_response.headers["location"]).to eq("/bar")
+      end
     end
 
     describe "with ambiguous routes and all matching" do