Plot of predictions with test data in Colab notebook doesn't make much sense

In the Colab notebook, after the training we plot some graphs.
The last one, which is "Plot the predictions along with to the test data", is literally taken from a standard TensorFlow Lite example notebook (see https://colab.research.google.com/github/tensorflow/tensorflow/blob/master/tensorflow/lite/experimental/micro/examples/hello_world/create_sine_model.ipynb#scrollTo=L_vE-ZDkHVxe )
but does not make much sense in this context.

Besides that, the code for that plot currently (ab)uses a deprecated matplotlib behaviour
```
/usr/local/lib/python3.6/dist-packages/matplotlib/axes/_base.py:380: MatplotlibDeprecationWarning:
cycling among columns of inputs with non-matching shapes is deprecated.
```
which also suggests that the current plot is a bit nonsensical.

Colab notebookを開き、リンク先のTensorFlow Liteの例と比較しながら、最後の「Plot the predictions along with to the test data」セクションを確認します。notebookをtrainingまで実行し、報告されているMatplotlibのdeprecation warningが発生しないように、test dataとpredictionsを意味のある形で表すplotに修正します。

索引モデルが issue の本文から書いたものです。