Fix appveyor failure cache not being expired

[bf4]

Fixes #1130

The cache isn't being expired:

def render_object_expired_with_cache_enabled
  generate_cached_serializer(post)
  post.title = 'ZOMG a New Post' # new title will only show up if cache expired
  sleep 0.1
  render json: post
end

 def test_render_with_cache_enable_and_expired
        ActionController::Base.cache_store.clear
        get :render_object_expired_with_cache_enabled

        expected = {
          id: 1,
          title: 'ZOMG a New Post',... # expect the new title
end
PostSerializer = Class.new(ActiveModel::Serializer) do
  cache key: 'post', expires_in: 0.1, skip_digest: true
....

 1) Failure:
ActionController::Serialization::ImplicitSerializerTest#test_cache_expiration_on_update 
[C:/projects/active-model-serializers/test/action_controller/serialization_test.rb:394]:
--- expected
+++ actual
@@ -1 +1 @@
-"{\"id\":1,\"title\":\"ZOMG a New Post\",
  \"body\":\"Body\",\"comments\":[{\"id\":1,\"body\":\"ZOMG A COMMENT\"}],\"blog\":{\"id\":999,\"name\":\"Custom blog\"},\"author\":{\"id\":1,\"name\":\"Joao Moura.\"}}"
+"{\"id\":1,\"title\":\"New Post\",
  \"body\":\"Body\",\"comments\":[{\"id\":1,\"body\":\"ZOMG A COMMENT\"}],\"blog\":{\"id\":999,\"name\":\"Custom blog\"},\"author\":{\"id\":1,\"name\":\"Joao Moura.\"}}"

[bf4]

well, at least I removed the sleep

[beauby]

👍