Fix json-pure's Object#to_json to accept non state arguments

Fix: ruby#573

CHANGES.md

@@ -1,6 +1,7 @@
 # Changes
 
 * Numerous performance optimizations in `JSON.generate` and `JSON.dump`.
+* Fix json-pure's `Object#to_json` to accept non state arguments 
 * Fix multiline comment support in `json-pure`.
 * Fix `JSON.parse` to no longer mutate the argument encoding when passed an ASCII-8BIT string.
 * Fix `String#to_json` to raise on invalid encoding in `json-pure`.

lib/json/pure/generator.rb

@@ -378,8 +378,8 @@ module Object
           # Converts this object to a string (calling #to_s), converts
           # it to a JSON string, and returns the result. This is a fallback, if no
           # special method #to_json was defined for some object.
-          def to_json(generator_state)
-            if generator_state.strict?
+          def to_json(state = nil, *)
+            if state && State.from_state(state).strict?
               raise GeneratorError, "#{self.class} not allowed in JSON"
             else
               to_s.to_json