update function arity in deprecation warning

Author: cgerling

lib/finch.ex

@@ -287,7 +287,7 @@ defmodule Finch do
   end
 
   def request(name, method, url, headers, body \\ nil, opts \\ []) do
-    IO.warn("Finch.request/6 is deprecated, use Finch.build/4 + Finch.request/3 instead")
+    IO.warn("Finch.request/6 is deprecated, use Finch.build/5 + Finch.request/3 instead")
 
     build(method, url, headers, body)
     |> request(name, opts)