title: Tensorflow federated can't be imported on google collabs notebook
body: <p>I wrote following codes on a new google collabs notebook:</p>
  <pre><code>!pip install --quiet --upgrade tensorflow-federated-nightly
  
  import tensorflow as tf
  import tensorflow_federated as tff
  </code></pre>
  <p>And I got these error messages while importing <code>tensorflow_federeated</code>:</p>
  <pre><code>/usr/local/lib/python3.7/dist-packages/keras/api/_v1/keras/experimental/__init__.py in &lt;module&gt;()
        8 from keras.feature_column.sequence_feature_column import SequenceFeatures
        9 from keras.layers.rnn.lstm_v1 import PeepholeLSTMCell
  ---&gt; 10 from keras.optimizers.learning_rate_schedule import CosineDecay
       11 from keras.optimizers.learning_rate_schedule import CosineDecayRestarts
       12 from keras.premade_models.linear import LinearModel
  
  ModuleNotFoundError: No module named 'keras.optimizers.learning_rate_schedule'; 'keras.optimizers' is not a package
  </code></pre>
  <p>These errors seem to be spawning from the modules installed on the colabs itself, instead of my code.
  <br/>Any idea on what can be done to fix this?</p>