escape the * of the generator function note to fix formatting

[chewiebug]

Reading this chapter on github in asciidoc format, I found that in the beginning of the "Generator Functions and Generator Objects* section, a "*" was not escaped properly, so that the rest of the text was rendered bold:

Checking locally with asciidoctor, only the rest of the line was rendered bold:

I have added an escape sequence to properly show the "*" and not have anything rendered in bold, that shouldn't.

[bevacqua]

Thanks, although I might revert if this renders improperly on other places (same files are used to render pdf, ebook, mobi, html, plus the versions on ponyfoo.com and on GitHub)

[bevacqua]

Looking good on https://ponyfoo.com/books/practical-modern-javascript/chapters/4#generator-fundamentals-nEsOfKul

🎉

[bevacqua]

Actually, it renders the + signs, so I'll need to revert.

[bevacqua]

Cool, doing pass:[<code>*</code>] worked as expected everywhere 🎉