Update knowledge_distillation.md

doc/doc_ch/knowledge_distillation.md

@@ -569,7 +569,7 @@ all_params = paddle.load("ch_PP-OCRv2_det_distill_train/best_accuracy.pdparams")
 # 查看权重参数的keys
 print(all_params.keys())
 # 学生模型的权重提取
-s_params = {key[len("Student."):]: all_params[key] for key in all_params if "Student." in key}
+s_params = {key[len("student_model."):]: all_params[key] for key in all_params if "student_model." in key}
 # 查看学生模型权重参数的keys
 print(s_params.keys())
 # 保存