Improve Flow enums comments formatting

[gkz]

I need to fix the formatting of comments in Flow enums (added in #6833). Not sure why it isn't working as expected.

Prettier /next/
Playground link

Input:

enum E {
  A = 0,
  // B = 1,
  C = 2
}

Output:

enum E {
// B = 1,
  A = 0,
  C = 2
}

Expected behavior:

enum E {
  A = 0,
  // B = 1,
  C = 2
}