def artifact(name, version)
      unless artifact?(name, version)
        artifact = Artifact.new(self, name, version)
        @artifacts["#{name}-#{version}"] = artifact
        @artifacts_by_name[name] << artifact
      end

      @artifacts["#{name}-#{version}"]
    end
def artifact(name, version)
      unless artifact?(name, version)
        artifact = Artifact.new(self, name, version)
        @artifacts["#{name}-#{version}"] = artifact
        @artifacts_by_name[name] << artifact
      end

      @artifacts["#{name}-#{version}"]
    end
Add an artifact to the graph

 @param [String] name
 @Param [String] version