Fix error of not founding tf_keras module (#13534)

Author: ceme393

research/audioset/yamnet/README.md

@@ -15,7 +15,7 @@ YAMNet depends on the following Python packages:
 * [`numpy`](http://www.numpy.org/)
 * [`resampy`](http://resampy.readthedocs.io/en/latest/)
 * [`tensorflow`](http://www.tensorflow.org/)
-* [`tf_keras`](https://github.com/keras-team/tf-keras)
+* [`tf-keras`](https://github.com/keras-team/tf-keras)
 * [`pysoundfile`](https://pysoundfile.readthedocs.io/)
 
 These are all easily installable via, e.g., `pip install numpy` (as in the
@@ -39,7 +39,7 @@ Here's a sample installation and test session:
 python -m pip install --upgrade pip wheel
 
 # Install dependences.
-pip install numpy resampy tensorflow soundfile
+pip install numpy resampy tensorflow soundfile tf-keras
 
 # Clone TensorFlow models repo into a 'models' directory.
 git clone https://github.com/tensorflow/models.git