Fix a comment

kernel/modelverse_jit/jit.py

@@ -232,7 +232,7 @@ class AnalysisState(object):
         #                        ("CD", [user_root, "last_output", new_last_output]),
         #                        ("DE", [last_output_link])
         #                       ]
-        # yield 'nop'
+        # yield None
 
         value_id, = yield [("RD", [instruction_id, "value"])]
         gen = self.analyze(value_id)