re-enable scala-native test

[xuwei-k]

• https://github.com/atnos-org/eff/commit/e49fe043e614d6264c1f8cdc02495ff5d9edff8a
• https://github.com/etorreborre/specs2/issues/1239
• https://github.com/atnos-org/eff/blob/e49fe043e614d6264c1f8cdc02495ff5d9edff8a/build.sbt#L287-L290

[xuwei-k]

• https://github.com/etorreborre/specs2/pull/1242
• https://github.com/etorreborre/specs2/pull/1241