Upgrade http.rb gem to 5.0.4.

Fixes a bug where the Foundation source strategy failed because http.rb
automatically sent a `Content-Length: 0` header with all GET requests,
which caused Foundation to return a 400 Bad Request error. This behavior
was fixed in http.rb 5.x.

http.rb 5.x has a breaking change where it now includes the request object
inside the response object, which we have to handle in a few places.

test/test_helpers/iqdb_test_helper.rb

@@ -1,7 +1,7 @@
 module IqdbTestHelper
   def mock_iqdb_matches(matches)
     Danbooru.config.stubs(:iqdb_url).returns("http://localhost:5588")
-    response = HTTP::Response.new(status: 200, body: matches.to_json, headers: { "Content-Type": "application/json" }, version: "1.1")
+    response = HTTP::Response.new(status: 200, body: matches.to_json, headers: { "Content-Type": "application/json" }, version: "1.1", request: nil)
     HTTP::Client.any_instance.stubs(:post).returns(response)
   end
 end

test/test_helpers/reportbooru_helper.rb

@@ -1,6 +1,6 @@
 module ReportbooruHelper
   def mock_request(url, method: :get, status: 200, body: nil, http: Danbooru::Http.any_instance, **options)
-    response = HTTP::Response.new(status: status, body: body, version: "1.1")
+    response = HTTP::Response.new(status: status, body: body, version: "1.1", request: nil)
     http.stubs(method).with(url, **options).returns(response)
   end