Updated api/v3.py for APIv3 resource name changes

PuppetDB APIv3 from APIv2 has 2 keys within the resource
endpoint have been changed.
'sourcefile' has been changed to 'file'
'sourceline' has been changed to 'line'

This patch allows pypuppetdb to	read resources from APIv3.

ref:
http://docs.puppetlabs.com/puppetdb/1.5/api/query/v3/resources.html#response-f\
ormat