Fix handle jest v27 fake timers (issue #30)

[wilsonpage]

The existing check for jest fake timers no longer works as jest v27 mutates the setTimeout global differently. This patch checks for both the old and new formats.

[lgandecki]

Thanks, do you think this works too? #37

I like that it also upgrades the jest so the tests verify the change

[wilsonpage]

Thanks, do you think this works too? #37

I like that it also upgrades the jest so the tests verify the change

👍 Looks like a better PR. You should merge that one.