added padding to Mirabelle's output

--- a/src/HOL/Tools/Mirabelle/mirabelle.scala	Fri Nov 12 00:28:00 2021 +0100
+++ b/src/HOL/Tools/Mirabelle/mirabelle.scala	Fri Nov 12 08:51:45 2021 +0100
@@ -87,7 +87,7 @@
                     Export.explode_name(args.name) match {
                       case List("mirabelle", action, "finalize") => action + " finalize  "
                       case List("mirabelle", action, "goal", goal_name, line, offset) =>
-                        action + " goal." + goal_name + " " + args.theory_name + " " +
+                        action + " goal." + String.format("%-5s", goal_name) + " " + args.theory_name + " " +
                           line + ":" + offset + "  "
                       case _ => ""
                     }