Fix minor grammar issues in chapter 3 of Async & Performance

[ghost]

Hello,

Just offering suggestions for some minor grammar issues I came across while reading this chapter 3 of the Async & Performance book. Specifically,

• Rewording: which more has our attention at present to which has more of our attention at present
• Hyphen removal to be consistent with word usage: reason-able to reasonable

[getify]

The first change is slight but reasonable. However, the second change shifts meaning away from intent. "reasonable" commonly means "acceptable", but "reason-able" means "able to be reasoned about".

[ghost]

@getify, understood—I've redacted that second change.

[kricketune]

The word promisory should also be changed to promissory. He said promisory was an actual word, but I can't find it in any dictionary.

[getify]

There's already a logged issue to handle the difference in spelling of promisory vs promissory.