Fails to parse corefn.json with 0.15.3

`$ zephyr -f Main.main`
```
Error: Failed parsing:
  output/Data.TraversableWithIndex/corefn.json
        output/Data.Semigroup.Last/corefn.json
        output/Control.Monad.Rec.Class/corefn.json
        output/Data.Monoid.Generic/corefn.json
        output/Data.Show.Generic/corefn.json
        ... (139 more)
```