Fix error in json deserialize demo

should return obj after setting all attrbutes.

source/c06/p02_read-write_json_data.rst

@@ -209,7 +209,7 @@ JSON编码的格式对于Python语法而已几乎是完全一样的，除了一
             obj = cls.__new__(cls) # Make instance without calling __init__
             for key, value in d.items():
                 setattr(obj, key, value)
-                return obj
+            return obj
         else:
             return d