Adds header as an option to new_request

This had to be done instead of extracting out the headers in options for
all functions that call request.

lib/stripe/request.ex

@@ -44,6 +44,11 @@ defmodule Stripe.Request do
   """
   @spec new_request(Stripe.options(), map) :: t
   def new_request(opts \\ [], headers \\ %{}) do
+    headers =
+      opts
+      |> Keyword.get(:headers, %{})
+      |> Map.merge(headers)
+
     %Request{opts: opts, headers: headers}
   end
 

test/stripe/request_test.exs

@@ -27,4 +27,14 @@ defmodule Stripe.RequestTest do
       assert request.opts == opts
     end
   end
+
+  describe "new_request/2" do
+    test "new_request/1 extracts headers from options and puts it on headers" do
+      new_request = Request.new_request(headers: %{foo: "bar"})
+
+      assert new_request.headers == %{
+               foo: "bar"
+             }
+    end
+  end
 end