prosodyctl: Fix using variable content in a format string

This broke if the error message contained a format specified such as '%s'.

1 files changed, 1 insertions, 1 deletions

diff --git a/prosodyctl b/prosodyctl
index 35c06220..e769ed5d 100755
--- a/prosodyctl
+++ b/prosodyctl
@@ -669,7 +669,7 @@ local command_runner = async.runner(function ()
 			end
 			os.exit(0, true); -- :)
 		else
-			show_message("Failed to execute command: "..error_messages[ret]);
+			show_message("Failed to execute command: %s", error_messages[ret]);
 			os.exit(1); -- :(
 		end
 	end