Update Enums.md: Fix wrong description

[green961]

in this section
Union enums and enum member types

enum E {
  Foo,
  Bar,
}

function f(x: E) {
  if (x !== E.Foo || x !== E.Bar) {

In that example, we first checked whether x was not E.Foo. If that check succeeds, then our || will short-circuit, and the body of the ‘if’ will run. However, if the check didn’t succeed, then x can only be E.Bar, so it doesn’t make sense to see whether it’s equal to E.Bar.

when the first check didn’t succeed, then x is E.Foo, so it doesn’t make sense to see x !== E.Bar

[0xScratch]

Now that's correct!!
But do provide some description and a valid 'heading' or 'commit line' for pull requests, easy for others to review

[jakebailey]

Presumably, #2868 was in fact wrong?

[jakebailey]

Yeah, I think I misread the other PR, as did the other author.