fix typo

Author: chenyushuo

trinity/algorithm/sample_strategy/mix_sample_strategy.py

@@ -114,12 +114,12 @@ def default_args(cls) -> Dict:
 
     def state_dict(self) -> dict:
         return {
-            "usal_buffer": self.usual_exp_buffer.state_dict(),
+            "usual_buffer": self.usual_exp_buffer.state_dict(),
             "expert_buffer": self.expert_exp_buffer.state_dict(),
         }
 
     def load_state_dict(self, state_dict: dict) -> None:
-        if state_dict.get("usal_buffer", None):
-            self.usual_exp_buffer.load_state_dict(state_dict["usal_buffer"])
+        if state_dict.get("usual_buffer", None):
+            self.usual_exp_buffer.load_state_dict(state_dict["usual_buffer"])
         if state_dict.get("expert_buffer", None):
             self.expert_exp_buffer.load_state_dict(state_dict["expert_buffer"])