code: function generateVersionArray(upgrade) {
    return _.map(_.keys(upgrade), function (version) {
      return parseFloat(version);
    }).sort(sortNumber);
  }
docs: Make an array of version numbers (that can include a decimal)
  and order them from least to greatest. The numbers are derived
  from the keys of the upgrade module that is required in.
  
  @param  {Object} upgrade
  @return {Array}