zig interpreter example seems to be broken in main

```
zig build -Dlang=lua54 run-example-interpreter
```

Out of the box, prints nothing.  I think this can be fixed by adding 

```
while (true) {
         _ = try stdout.writeAll("> ");
+        try stdout.flush();
```

This makes it print 

`> `

but nothing happens after that no matter what I write in the interpreter.  

I'm on macOS.
