Purescript: Instances with just one method do not require that the method be indented

[rightfold]

That is, the following compiles:

data Unit = Unit

instance eqUnit :: Eq Unit where
eq _ _ = true

[quesebifurcan]

New contributor here -- I'd be happy to give this one a try.

[kpadmasola]

@paf31 , New contributor here -- I'd be happy to give this one a try. What more is needed here?

[paf31]

@kpadmasola There was a previous PR for this, which I need to include in the changes for 0.12.0.

https://github.com/purescript/purescript/pull/2965

Thank you though, and if you're interested in finding something else to work on, maybe we can help on Slack.