Tight layout for figures in torchaudio tutorial

[vincentqb]

Some figures in the torchaudio tutorial have a wide aspect ratio, but are displayed with a lot of white space above and below them as if they were square.

• When downloading an image from the rendered HTML, the white is part of it.
• plt.tight_layout() does not address that.

CC @fbbradheintz

[vincentqb]

@cpuhrsch @jamarshon

[carljparker]

Looks as though this is fixed by Update audio preprocessing tutorial #797