code: public GitlabMilestone updateMilestone(
              GitlabMilestone edited,
              String stateEvent)
              throws IOException {
          return updateMilestone(edited.getProjectId(), edited, stateEvent);
      }
docs: Updates an existing project milestone.
  
  @param edited     The already edited milestone.
  @param stateEvent A value used to update the state of the milestone.
  (Optional) (activate | close)
  @return The updated, de-serialized milestone.
  @throws IOException on gitlab api call error