migration.js

exports.up = function(knex) {
  knex('users')
    .update({
      language: users.get('language') + '-' + users.get('country')
    })
    .dropColumn('country')
    .column('language').defaultTo('en-US')
};

exports.down = function(knex) {
  knex('users')
    .addColumn('country')
    .update({
      country: users.language.slice(0,1),
      language: users.language.slice(3,4)
    })
};