JDK 11 fixes

In JDK 11, String.lines returns java.util.stream.Stream[String]. Switch
to linesIterator instead.

main/src/main/scala/sbt/internal/LayeredClassLoader.scala

@@ -43,7 +43,7 @@ private[sbt] class LayeredClassLoader(
   |  classpath =
   |    ${classpath mkString "\n    "}
   |  parent =
-  |    ${parent.toString.lines.mkString("\n    ")}
+  |    ${parent.toString.linesIterator.mkString("\n    ")}
   |)""".stripMargin
 }
 

main/src/main/scala/sbt/internal/PrettyPrint.scala

@@ -10,6 +10,6 @@ package sbt.internal
 private[sbt] object PrettyPrint {
   private[sbt] def indent(any: Any, level: Int): String = {
     val i = " " * level
-    any.toString.lines.mkString(i, "\n" + i, "")
+    any.toString.linesIterator.mkString(i, "\n" + i, "")
   }
 }