code: function validSemverTag(list, tag) {
      if (semver.valid(tag)) {
          list.push(tag);
      }
  
      return list;
  }
docs: Push supplied `tag` to supplied `list` only if it is a valid semver. This is
  a reducer function.
  
  @private
  @param  {Array}  list - array of valid semver tags
  @param  {String} tag  - tag to push if valid
  @returns {Array}  modified `list`