Ch 3, worth mentioning about 'not_to' and 'to_not'

[JunichiIto]

I found you use not_to instead of to_not from RSpec 3 edition and I am wondering why.

But anyway I think it is worth mentioning about not_to and to_not. Readers should know they can use both. If there is any rule to determine which to use, I would like to know it.

[JunichiIto]

In chapter 5 and chapter 11, to_not still exists. Please grep and fix them for consistency.

[ruralocity]

I changed them to match RSpec's documentation more closely. I've updated the book for consistency and will update the example repo before releasing an update.