Fixed Broken Links

Switch `official/nlp/bert` to `official/legacy/bert` for open sourced model garden.

docs/nlp/index.ipynb

@@ -306,7 +306,7 @@
       },
       "source": [
         "With the loss, you can optimize the model.\n",
-        "After training, we can save the weights of TransformerEncoder for the downstream fine-tuning tasks. Please see [run_pretraining.py](https://github.com/tensorflow/models/blob/master/official/nlp/bert/run_pretraining.py) for the full example.\n"
+        "After training, we can save the weights of TransformerEncoder for the downstream fine-tuning tasks. Please see [run_pretraining.py](https://github.com/tensorflow/models/blob/master/official/legacy/bert/run_pretraining.py) for the full example.\n"
       ]
     },
     {
@@ -426,7 +426,7 @@
         "id": "Zdf03YtZmd_d"
       },
       "source": [
-        "With the `loss`, you can optimize the model. Please see [run_squad.py](https://github.com/tensorflow/models/blob/master/official/nlp/bert/run_squad.py) for the full example."
+        "With the `loss`, you can optimize the model. Please see [run_squad.py](https://github.com/tensorflow/models/blob/master/official/legacy/bert/run_squad.py) for the full example."
       ]
     },
     {
@@ -538,7 +538,7 @@
         "id": "mzBqOylZo3og"
       },
       "source": [
-        "With the `loss`, you can optimize the model. Please see [run_classifier.py](https://github.com/tensorflow/models/blob/master/official/nlp/bert/run_classifier.py) or the [Fine tune_bert](https://www.tensorflow.org/text/tutorials/fine_tune_bert) notebook for the full example."
+        "With the `loss`, you can optimize the model. Please see [run_classifier.py](https://github.com/tensorflow/models/blob/master/official/legacy/bert/run_classifier.py) or the [Fine tune_bert](https://www.tensorflow.org/text/tutorials/fine_tune_bert) notebook for the full example."
       ]
     }
   ],