[doc] update aishell url

follow #2205

docs/pretrained_models.en.md

@@ -18,7 +18,7 @@ Here is a list of the pretrained models on different datasets. The model structu
 
 | Datasets  | Languages     | Checkpoint Model  | Runtime Model     | Contributor |
 |---    |---    |---    |---    |---    |
-| [aishell](../examples/aishell/s0/README.md)   | CN    | [Conformer](https://wenet.org.cn/downloads?models=wenet&version=aishell_u2pp_conformer_exp.tar.gz)  | [Conformer](https://wenet.org.cn/downloads?models=wenet&version=aishell_u2pp_conformer_libtorch.tar.gz)     | <a href="https://www.chumenwenwen.com" target="_blank"><img src="https://raw.githubusercontent.com/wenet-e2e/wenet-contributors/main/companies/chumenwenwen.png" width="100px"></a> |
+| [aishell](../examples/aishell/s0/README.md)   | CN    | [Conformer](https://wenet.org.cn/downloads?models=wenet&version=20210601_u2++_conformer_exp_aishell.tar.gz)  | [Conformer](https://wenet.org.cn/downloads?models=wenet&version=20210601_u2++_conformer_libtorch_aishell.tar.gz)     | <a href="https://www.chumenwenwen.com" target="_blank"><img src="https://raw.githubusercontent.com/wenet-e2e/wenet-contributors/main/companies/chumenwenwen.png" width="100px"></a> |
 | [aishell2](../examples/aishell2/s0/README.md)     | CN    | [Conformer](https://wenet.org.cn/downloads?models=wenet&version=aishell2_u2pp_conformer_exp.tar.gz)     | [Conformer](https://wenet.org.cn/downloads?models=wenet&version=aishell2_u2pp_conformer_libtorch.tar.gz)    | <a href="https://www.chumenwenwen.com" target="_blank"><img src="https://raw.githubusercontent.com/wenet-e2e/wenet-contributors/main/companies/chumenwenwen.png" width="100px"></a> |
 | [gigaspeech](../examples/gigaspeech/s0/README.md)     | EN    | [Conformer](https://wenet.org.cn/downloads?models=wenet&version=gigaspeech_u2pp_conformer_exp.tar.gz)   | [Conformer](https://wenet.org.cn/downloads?models=wenet&version=gigaspeech_u2pp_conformer_libtorch.tar.gz)  |  <a href="https://www.chumenwenwen.com" target="_blank"><img src="https://raw.githubusercontent.com/wenet-e2e/wenet-contributors/main/companies/chumenwenwen.png" width="100px"></a> |
 | [librispeech](../examples/librispeech/s0/README.md)   | EN    | [Conformer](https://wenet.org.cn/downloads?models=wenet&version=librispeech_u2pp_conformer_exp.tar.gz)  | [Conformer](https://wenet.org.cn/downloads?models=wenet&version=librispeech_u2pp_conformer_libtorch.tar.gz)     |  <a href="https://www.chumenwenwen.com" target="_blank"><img src="https://raw.githubusercontent.com/wenet-e2e/wenet-contributors/main/companies/chumenwenwen.png" width="100px"></a> |