MultiWayIf: Expects different indentation than GHC

Consider this file:
```
{-# LANGUAGE MultiWayIf #-}

foo b = if | b
           , b
           -> 1
           | otherwise
           -> 2
```
It loads in ghc, but haskell-src-exts say
```
ghci> Language.Haskell.Exts.parseFile "/tmp/Test.hs"
ParseFailed (SrcLoc "/tmp/Test.hs" 4 12) "Parse error: ;"
```

It works if I indent the lines starting with `,` and `->` by at least one space.