Fix Meterpreter PHP hop description

If you interpret `File` locations for things in descriptions, you end up with wonky looking paths. For example:

http://www.rapid7.com/db/modules/payload/windows/meterpreter/reverse_hop_http

Incidentally, the canonical way to refer to paths of Metasploit assets are the methods in `Msf::Config`. That's how datastore directories are built, anyway (and still not really appropriate for descriptions).