webfinger: send JRD by default instead of XRD

JRD being the default representation for WebFinger responses was standardized 5 years ago in
RFC 7033.

lib/pleroma/web/router.ex

@@ -41,7 +41,7 @@ def user_fetcher(username) do
   end
 
   pipeline :well_known do
-    plug(:accepts, ["xml", "xrd+xml", "json", "jrd+json"])
+    plug(:accepts, ["json", "jrd+json", "xml", "xml+xrd"])
   end
 
   pipeline :config do