Update slim include. (#8036)

* Update slim include.

* Force installation of tensorflow 1.14 (not tf2).

research/audioset/vggish/README.md

@@ -63,7 +63,8 @@ $ sudo python -m pip install --upgrade pip
 # Install dependences. Resampy needs to be installed after NumPy and SciPy
 # are already installed.
 $ sudo pip install numpy scipy soundfile
-$ sudo pip install resampy tensorflow six
+$ sudo pip install resampy six
+$ sudo pip install tensorflow==1.14
 
 # Clone TensorFlow models repo into a 'models' directory.
 $ git clone https://github.com/tensorflow/models.git

research/audioset/vggish/vggish_slim.py

@@ -30,10 +30,11 @@ For comparison, here is TF-Slim's VGG definition:
 https://github.com/tensorflow/models/blob/master/research/slim/nets/vgg.py
 """
 
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
+from tensorflow.contrib import slim as contrib_slim
 import vggish_params as params
 
-slim = tf.contrib.slim
+slim = contrib_slim
 
 
 def define_vggish_slim(training=False):