Remove reference to Slack.
@@ -193,7 +193,6 @@ You can ask questions and join the development discussion:
- In the [TensorFlow forum](https://discuss.tensorflow.org/).
- On the [Keras Google group](https://groups.google.com/forum/#!forum/keras-users).
-- On the [Keras Slack channel](https://kerasteam.slack.com). Use [this link](https://keras-slack-autojoin.herokuapp.com/) to request an invitation to the channel.
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