adding more methods necessary for the faraday adapter when it comes to multi-response errors

lib/httpx/response.rb

@@ -269,6 +269,14 @@ module HTTPX
       @error.message
     end
 
+    def reason
+      @error.class.name
+    end
+
+    def headers
+      {}
+    end
+
     def body
       @error.backtrace.join("\n")
     end

test/error_response_test.rb

@@ -18,7 +18,7 @@ class ErrorResponseTest < Minitest::Test
 
   def test_respond_method_missing_errors
     r1 = ErrorResponse.new(Minitest::Mock.new, RuntimeError.new("wow"), {})
-    ex1 = assert_raises(NoMethodError) { r1.headers }
+    ex1 = assert_raises(NoMethodError) { r1.read }
     assert ex1.message =~ /undefined response method/
     ex2 = assert_raises(NoMethodError) { r1.bang }
     assert ex2.message =~ /undefined method/