Embed objects should return singular and not wrap in array

Closes #437

test/integration/active_record/active_record_test.rb

@@ -17,7 +17,7 @@ module ActiveModel
             ar_comments: [{ body: 'what a dumb post', ar_tags: [{ name: 'short' }, { name: 'whiny' }] },
                           { body: 'i liked it', ar_tags: [{:name=>"short"}, {:name=>"happy"}] }],
             ar_tags: [{ name: 'short' }, { name: 'whiny' }, { name: 'happy' }],
-            'ar_sections' => [{ 'name' => 'ruby' }]
+            ar_section: { 'name' => 'ruby' }
           }
         }, post_serializer.as_json)
       end

test/unit/active_model/serializer/has_one_test.rb

@@ -50,7 +50,7 @@ module ActiveModel
         @association.embed = :objects
 
         assert_equal({
-          name: 'Name 1', email: 'mail@server.com', 'profiles' => [{ name: 'N1', description: 'D1' }]
+          name: 'Name 1', email: 'mail@server.com', profile: { name: 'N1', description: 'D1' }
         }, @user_serializer.serializable_hash)
       end
 
@@ -58,7 +58,7 @@ module ActiveModel
         @association.embed = :objects
 
         assert_equal({
-          'user' => { name: 'Name 1', email: 'mail@server.com', 'profiles' => [{ name: 'N1', description: 'D1' }] }
+          'user' => { name: 'Name 1', email: 'mail@server.com', profile: { name: 'N1', description: 'D1' } }
         }, @user_serializer.as_json)
       end
 
@@ -84,7 +84,7 @@ module ActiveModel
         end
 
         assert_equal({
-          'user' => { name: 'Name 1', email: 'mail@server.com', 'profiles' => [] }
+          'user' => { name: 'Name 1', email: 'mail@server.com', profile: nil }
         }, @user_serializer.as_json)
       end
 
@@ -93,7 +93,7 @@ module ActiveModel
         @association.embedded_key = 'root'
 
         assert_equal({
-          name: 'Name 1', email: 'mail@server.com', 'root' => [{ name: 'N1', description: 'D1' }]
+          name: 'Name 1', email: 'mail@server.com', 'root' => { name: 'N1', description: 'D1' }
         }, @user_serializer.serializable_hash)
       end