fix skylight normalizers issue

lib/fast_jsonapi/instrumentation/skylight/normalizers/base.rb

@@ -0,0 +1,7 @@
+require 'skylight'
+
+SKYLIGHT_NORMALIZER_BASE_CLASS = begin
+  ::Skylight::Core::Normalizers::Normalizer
+rescue NameError
+  ::Skylight::Normalizers::Normalizer
+end

lib/fast_jsonapi/instrumentation/skylight/normalizers/serializable_hash.rb

@@ -1,11 +1,11 @@
-require 'skylight'
+require 'fast_jsonapi/instrumentation/skylight/normalizers/base'
 require 'fast_jsonapi/instrumentation/serializable_hash'
 
 module FastJsonapi
   module Instrumentation
     module Skylight
       module Normalizers
-        class SerializableHash < Skylight::Normalizers::Normalizer
+        class SerializableHash < SKYLIGHT_NORMALIZER_BASE_CLASS
 
           register FastJsonapi::ObjectSerializer::SERIALIZABLE_HASH_NOTIFICATION
 

lib/fast_jsonapi/instrumentation/skylight/normalizers/serialized_json.rb

@@ -1,11 +1,11 @@
-require 'skylight'
+require 'fast_jsonapi/instrumentation/skylight/normalizers/base'
 require 'fast_jsonapi/instrumentation/serializable_hash'
 
 module FastJsonapi
   module Instrumentation
     module Skylight
       module Normalizers
-        class SerializedJson < Skylight::Normalizers::Normalizer
+        class SerializedJson < SKYLIGHT_NORMALIZER_BASE_CLASS
 
           register FastJsonapi::ObjectSerializer::SERIALIZED_JSON_NOTIFICATION
 

spec/lib/instrumentation/skylight/normalizers_require_spec.rb

@@ -0,0 +1,14 @@
+require 'spec_helper'
+
+describe FastJsonapi::ObjectSerializer do
+
+  context 'instrument' do
+    context 'skylight' do
+      # skip for normal runs because this could alter some
+      # other test by insterting the instrumentation
+      xit 'make sure requiring skylight normalizers works' do
+        require 'fast_jsonapi/instrumentation/skylight'
+      end
+    end
+  end
+end