tuned message;

--- a/src/Pure/System/isabelle_system.scala	Fri May 07 23:56:18 2021 +0200
+++ b/src/Pure/System/isabelle_system.scala	Sat May 08 00:31:51 2021 +0200
@@ -300,7 +300,7 @@
       }
       catch {
         case ERROR(msg) =>
-          cat_error("Failed top copy file " +
+          cat_error("Failed to copy file " +
             File.path(src).absolute + " to " + File.path(dst).absolute, msg)
       }
     }