util.prosodyctl.shell: Close state on exit to fix saving shell history

This ensures a last round of garbage collection and finalizers, which
should include flushing the readline history file.

Test procedure:
```
$ ./prosodyctl shell
prosody> s2s:show() -- any command that is not the last in history
... output
prosody> bye
$ ./prosodyctl shell
prosody> ^P
```

After this, the shell prompt should contain the last command from before
the "bye". Before this patch, recent history is gone most of the time.

1 files changed, 2 insertions, 2 deletions

diff --git a/util/prosodyctl/shell.lua b/util/prosodyctl/shell.lua
index bce27b94..8cf7df69 100644
--- a/util/prosodyctl/shell.lua
+++ b/util/prosodyctl/shell.lua
@@ -39,7 +39,7 @@ local function repl(client)
 		if have_readline then
 			readline.save_history();
 		end
-		os.exit();
+		os.exit(0, true);
 	end
 	send_line(client, line);
 end
@@ -112,7 +112,7 @@ local function start(arg) --luacheck: ignore 212/arg
 
 	client.events.add_handler("disconnected", function ()
 		print("--- session closed ---");
-		os.exit();
+		os.exit(0, true);
 	end);
 
 	client.events.add_handler("received", function (stanza)