formatter won't keep multiline for exceptions

[tx46]

how to test:

1. type type t = {name: string, msg: string} and run formatter
2. notice still single line
3. type

type t = {
  name: string,
  msg: string,
}

and run formattter 4. notice still four lines 5. type exception Foo({name: string,msg: string}) and run formatter 6. notice still single line 7. type

exception Foo({
  name: string,
  msg: string,
})

and run formatter 8. BUG: formatter forces it to single line