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.

打开 Colab notebook，检查最后的 "Plot the predictions along with to the test data" 部分，并将其与链接的 TensorFlow Lite 示例进行比较。运行 notebook 完成 training，并修改 plot，使其能够有意义地表示 test data 和 predictions，同时不再出现报告的 Matplotlib deprecation warning。

由索引模型根据 Issue 内容生成。