Rewrite for eta-expension

[MasseGuillaume]

One of the probably many paterns to rewrite (see scala/scala#6475 for more details):

class C(in: () => Int)
def f(): Int = 1

new C(f) // does not compile anymore in 2.13.0-M4

-new C(f)
+new C(() => f)

[SethTisue]

I tend to still write f _, but I guess in the long run that syntax is on its way out

[SethTisue]

(ironically, that syntax is on its way out because new C(f) is going to be made to work again...)