Danbooru::Http: redirect POST to GET on 302.

When a POST request returns a 302 redirect, follow the redirect with a
GET request instead of with a POST request.

HTTP standards leave it unspecified whether a POST request that returns
a 302 redirect should be followed with a GET or with a POST. A GET is
what most browsers use, which means it's what most servers expect.

Fixes the /tagme Discord command not working because when we uploaded
the image to DeepDanbooru, the POST request returned a 302 redirect,
which the server expected us to follow with a GET, not with a POST.

Ref:

* https://stackoverflow.com/questions/17605915/what-is-the-correct-behavior-expected-of-an-http-post-302-redirect-to-get

app/logical/danbooru/http/redirector.rb

@@ -31,7 +31,7 @@ module Danbooru
         uri = HTTP::URI.parse(location)
 
         verb = request.verb
-        verb = :get if response.status == 303 && !request.verb.in?([:get, :head])
+        verb = :get if response.status.in?([302, 303]) && !request.verb.in?([:get, :head])
 
         request.redirect(uri, verb)
       end