Update NAN reference in php parser
Update NAN reference in php parser

Confirmed via this helpful report that we're mis-referencing php's nan.
stderr gets flooded with notices. With this change, the notices go away
and everything seems to work.

https://github.com/codeclimate/codeclimate-duplication/issues/186#issuecomment-300775403

codeclimate/codeclimate-duplication,codeclimate/codeclimate-duplication,codeclimate/codeclimate-duplication,codeclimate/codeclimate-duplication