http: connection: merge hackney option lists instead of concatenating them

this ensures the right pools are used

lib/pleroma/http/connection.ex

@@ -31,6 +31,6 @@ def new(opts \\ []) do
   #
   defp hackney_options(opts) do
     options = Keyword.get(opts, :adapter, [])
-    @hackney_options ++ options
+    Keyword.merge(@hackney_options, options)
   end
 end