Fix crossed text in attention homework

[CrafterKolyan]

For now the text:
5 if you average over time, scale by length if you sum over time. The reasonable captions began appearing at loss=3.5
just gets crossed like this:

• The typical loss values should be around 35 if you average over time, scale by length if you sum over time. The reasonable captions began appearing at loss=3.53.7

This is due to Markdown used in Jupyter Notebook cells.
This pull request fixes this issue so it looks like:

• The typical loss values should be around 3~5 if you average over time, scale by length if you sum over time. The reasonable captions began appearing at loss=3.5~3.7