Autoinvite fix

Not really sure where to put this, I'm not a windower dev or official addon maker, but I tried to fix the autoinvite addon since it wasn't working, was failing to detect passed arguments correctly, seemed to be related to the use of isin() which the stringhelper.lua says is now deprecated. I've changed this over to a table.contains or a simple == where appropriate and all seems ok now. Are there any devs that can check the attached autoinvite.lua (renamed to autoinvite.txt so it'll let me upload) and upload or..?

You should submit a pull request on GitHub. That way we can merge in the change directly.