Enable color by default in ci builds

This channge should turn color on by default in ci builds (see
https://github.com/sbt/sbt/issues/5269). It can still be disabled with
-Dsbt.color=false.

internal/util-logging/src/main/scala/sbt/internal/util/Terminal.scala

@@ -314,7 +314,7 @@ object Terminal {
   private[this] def useColorDefault: Boolean = {
     // This approximates that both stdin and stdio are connected,
     // so by default color will be turned off for pipes and redirects.
-    props.map(_.color).orElse(isColorEnabledProp).getOrElse(hasConsole && !isDumbTerminal)
+    props.map(_.color).orElse(isColorEnabledProp).getOrElse((hasConsole && !isDumbTerminal) || isCI)
   }
   private[this] lazy val isColorEnabledProp: Option[Boolean] =
     sys.props.get("sbt.color").orElse(sys.props.get("sbt.colour")).flatMap(parseLogOption)