Update serializer.rb

Minor typos.

lib/active_model/serializer.rb

@@ -115,7 +115,7 @@ def self.attribute(attr, options = {})
 
     # @api private
     # Used by FragmentCache on the CachedSerializer
-    #  to call attribute methods on the fragmented cached serializer
+    #  to call attribute methods on the fragmented cached serializer.
     def self.fragmented(serializer)
       self._fragmented = serializer
     end
@@ -173,7 +173,7 @@ def self.adapter
     end
 
     # Used to cache serializer name => serializer class
-    # when looked up by Serializer.get_serializer_for
+    # when looked up by Serializer.get_serializer_for.
     def self.serializers_cache
       @serializers_cache ||= ThreadSafe::Cache.new
     end
@@ -200,8 +200,8 @@ def self.get_serializer_for(klass)
     class_attribute :_type, instance_writer: false
 
     # `scope_name` is set as :current_user by default in the controller.
-    # If the instance does not have a method nameed `scope_name`, it
-    # defines the method so that calls the +scope+.
+    # If the instance does not have a method named `scope_name`, it
+    # defines the method so that it calls the +scope+.
     def initialize(object, options = {})
       self.object = object
       self.instance_options = options
@@ -216,7 +216,7 @@ def initialize(object, options = {})
       end
     end
 
-    # Used by adapter as resource root
+    # Used by adapter as resource root.
     def json_key
       root || object.class.model_name.to_s.underscore
     end