Before this change, the scala compiler issued warnings such as the one
below, upon using the usual 'sbt compile' command.
"(...) postfix operator second should be enabled
[warn] by making the implicit value scala.language.postfixOps visible.
[warn] This can be achieved by adding the import clause 'import scala.language.postfixOps'
[warn] or by setting the compiler option -language:postfixOps."
Set the latter option in build.sbt to remove these warnings. This is
less invasive than adding the aforementioned import clause in each file.
Bug: Issue 12288
Change-Id: If52dcddbcc63579602c788455a95c5e7d9009ee2