bugfix: payload_path isn't an attr, breaks logging
bugfix: payload_path isn't an attr, breaks logging

In v1's _send_hook() method, I was calling payload_path as an
attribute, rather than the variable it is.

felliott/waterbutler,TomBaxter/waterbutler,RCOSDP/waterbutler,kwierman/waterbutler,rdhyee/waterbutler,Johnetordoff/waterbutler,CenterForOpenScience/waterbutler