Provide data to post call in Artifact.rb

Artifactory reads the query string rather than posted form data, but the client.post method still requires that data as an argument. Provide an empty hash.
Merge pull request #1 from swivelhinges/fix_copy_or_move

Provide data to post call in Artifact.rb
Merge pull request #45 from swivelhinges/master

Provide data to post call in Artifact.rb