FixRM:8716, session upgrade script

Doesn't appear to be any other issues similar following https://github.com/rapid7/metasploit-framework/pull/2426:

```root@kali:~/git/metasploit-framework# grep -r -i "data_directory, \"data" . ```

```./scripts/shell/spawn_meterpreter.rb:    :decoder => File.join(Msf::Config.data_directory, "data", "exploits", "cmdstager", "vbs_b64"),```

```root@kali:~/git/metasploit-framework# grep -r -i "data_directory, 'data" .```