Fix typo in comments

Author: bf4

lib/active_model/serializer.rb

@@ -34,7 +34,7 @@ def self.inherited(base)
     end
 
     # Primary interface to building a serializer (with adapter)
-    # If no block is given, returns the adapter, ready for #as_json/#to_json
+    # If no block is given, returns the builder, ready for #as_json/#to_json/#serializable_hash
     # Otherwise, yields the builder and returns the contents of the block
     def self.build(resource, options = {})
       builder = Builder.new(resource, options)