fix: add xblock 2.0 support (#359)

edx_sga/sga.py

@@ -181,7 +181,7 @@ def file_size_over_limit(cls, file_obj):
         return file_obj.tell() > cls.student_upload_max_size()
 
     @classmethod
-    def parse_xml(cls, node, runtime, keys, id_generator):
+    def parse_xml(cls, node, runtime, keys):
         # pylint: disable=arguments-differ,unused-argument
         """
         Override default serialization to handle <solution /> elements