old_contents: const Umzug = require('umzug');
  const sequelize = require('../db');
  const async = require('async');
  const path = require('path');
  
  const waterfall = ['cat','dog'].map((modelName) => {
      return (done) => {
          const migrations = { path: path.resolve(`./lib/${modelName}/migrations/`) };
          const umzug = new Umzug({ sequelize, migrations });
  
          umzug.down({ to: 0 }).then(function()  {
              console.log(`Undo migration complete for model: "${modelName}"`);
              done();
          }).catch(done);
      };
  });
  
  async.waterfall(waterfall, (err) => {
      if (err) {
          console.log('\n\nFail!', err);
      } else {
          console.log('\n\nUndo migration complete!');
      }
  });
  
new_contents: const async = require('async');
  
  const waterfall = ['cat','dog'].map((modelName) => {
      return (done) => {
          const umzug = require('./umzug').getInstance(tableName);
  
          umzug.down({ to: 0 }).then(function()  {
              console.log(`Undo migration complete for model: "${modelName}"`);
              done();
          }).catch(done);
      };
  });
  
  async.waterfall(waterfall, (err) => {
      if (err) {
          console.log('\n\nFail!', err);
      } else {
          console.log('\n\nUndo migration complete!');
      }
  });
  
subject: Update down to use umzug object