Change headers to be lower case in example application

Headers must be lowercase.

Author: sajmoon

examples/simpleapp/lib/simpleapp.ex

@@ -1,7 +1,7 @@
 defmodule Simpleapp do
   use Plug.Router
 
-  plug Mellon, validator: {Simpleapp, :authenticate, []}, header: "X-AUTH"
+  plug Mellon, validator: {Simpleapp, :authenticate, []}, header: "x-auth"
 
   plug :match
   plug :dispatch

examples/simpleapp/test/simpleapp_test.exs

@@ -13,7 +13,7 @@ defmodule SimpleappTest do
 
   test "denied if invalid token" do
     conn = conn(:get, "/hello")
-    |> put_req_header("X-AUTH", "Token: InvalidToken")
+    |> put_req_header("x-auth", "Token: InvalidToken")
     |> Simpleapp.call([])
 
     assert conn.state == :sent
@@ -23,7 +23,7 @@ defmodule SimpleappTest do
 
   test "denied if token form is wrong" do
     conn = conn(:get, "/hello")
-    |> put_req_header("X-AUTH", "")
+    |> put_req_header("x-auth", "")
     |> Simpleapp.call([])
 
     assert conn.state == :sent
@@ -33,7 +33,7 @@ defmodule SimpleappTest do
 
   test "/hello ok if correct credentials" do
     conn = conn(:get, "/hello")
-    |> put_req_header("X-AUTH", "Token: ValidToken")
+    |> put_req_header("x-auth", "Token: ValidToken")
     |> Simpleapp.call([])
 
     assert conn.state == :sent