Make sure UpdateReport has a nice toString^2

Fixes sbt/sbt#3357

core/src/main/scala/sbt/librarymanagement/UpdateReportExtra.scala

@@ -61,7 +61,7 @@ abstract class ModuleReportExtra {
     s"\t\t- ${module.revision}\n" +
       (if (arts.size <= 1) "" else arts.mkString("\t\t\t", "\n\t\t\t", "\n")) +
       reportStr("status", status) +
-      reportStr("publicationDate", publicationDate map { _.toString }) +
+      reportStr("publicationDate", publicationDate map calendarToString) +
       reportStr("resolver", resolver) +
       reportStr("artifactResolver", artifactResolver) +
       reportStr("evicted", Some(evicted.toString)) +
@@ -96,6 +96,11 @@ abstract class ModuleReportExtra {
       s"\t\t\t$key: $x\n"
     } getOrElse ""
 
+  private[this] def calendarToString(c: ju.Calendar): String = {
+    import sjsonnew._, BasicJsonProtocol._
+    implicitly[IsoString[ju.Calendar]] to c
+  }
+
   def retrieve(f: (ModuleID, Artifact, File) => File): ModuleReport =
     copy(artifacts = artifacts.map { case (art, file) => (art, f(module, art, file)) })
 

core/src/test/scala/UpdateReportSpec.scala

@@ -12,6 +12,7 @@ class UpdateReportSpec extends FlatSpec with Matchers {
       |	compile:
       |	org:name
       |		- 1.0
+      |			publicationDate: 1970-01-01T00:00:00Z
       |			evicted: false
       |
       |""".stripMargin.drop(1))
@@ -32,10 +33,18 @@ class UpdateReportSpec extends FlatSpec with Matchers {
       Vector(organizationArtifactReport)
     )
 
-  lazy val moduleReport =
+  lazy val moduleReport = (
     ModuleReport(ModuleID("org", "name", "1.0"), Vector.empty, Vector.empty)
+      withPublicationDate Some(epochCalendar)
+  )
 
   lazy val organizationArtifactReport =
     OrganizationArtifactReport("org", "name", Vector(moduleReport))
 
+  val epochCalendar: java.util.Calendar = {
+    val utc = java.util.TimeZone getTimeZone "UTC"
+    val c = new java.util.GregorianCalendar(utc, java.util.Locale.ENGLISH)
+    c setTimeInMillis 0L
+    c
+  }
 }