config/config.exs: Add application/jrd+json => jrd+json to fix webfinger

Closes: pleroma/pleroma!551

config/config.exs

@@ -65,6 +65,7 @@ config :logger, :console,
 config :mime, :types, %{
   "application/xml" => ["xml"],
   "application/xrd+xml" => ["xrd+xml"],
+  "application/jrd+json" => ["jrd+json"],
   "application/activity+json" => ["activity+json"],
   "application/ld+json" => ["activity+json"]
 }