using *zip*/archive.zip as default for :jenkins_artifact_file

deploy fails with `SSHKit::Runner::ExecuteError: Exception while executing on host <deploy host>: can't convert nil into String` when `:jenkins_artifact_file` not specified

using `*zip*/archive.zip` as default value

if `:jenkins_artifact_file` option not specified - unzipping artifact content and moving to release path.
Perhaps, instead of checking if `:jenkins_artifact_file` is `nil`, since it won’t be nil unless specifically set that way (which would break the deployment), this should check if `:jenkins_artifact_file` contains `zip`?

Clearly, not the only kind of archive possible, but goes hand-in-hand with this pull request’s apparent purpose.