add parentheses for lambda param

[xuwei-k]

Pull Request Checklist

• Have you read through the contributor guidelines?
• Have you signed the Typesafe CLA?
• Have you squashed your commits?
• Have you added copyright headers to new files?
• Have you checked that both Scala and Java APIs are updated?
• Have you updated the documentation for both Scala and Java sections?
• Have you added tests for any changed functionality?

Fixes

Purpose

prepare Scala 3

scala> Option(1).map{ a => a }
val res0: Option[Int] = Some(1)

scala> Option(1).map{ a: Int => a }
1 |Option(1).map{ a: Int => a }
  |                      ^
  |parentheses are required around the parameter of a lambda
  |This construct can be rewritten automatically under -rewrite -source 3.0-migration.

Background Context

References

[mkurz]

Thanks! I hijacked your branch to fix travis, so the tests pass 😉