fix: Fixed sequelize-cli db:migration cannot stop when occur error

Up and Down method must return a Promise.

breaking changes: docker-hackmd cannot initialize, because db:migration will fail

lib/migrations/20161201050312-support-email-signin.js

@@ -1,12 +1,14 @@
 'use strict'
 module.exports = {
   up: function (queryInterface, Sequelize) {
-    queryInterface.addColumn('Users', 'email', Sequelize.TEXT)
-    queryInterface.addColumn('Users', 'password', Sequelize.TEXT)
+    return queryInterface.addColumn('Users', 'email', Sequelize.TEXT).then(function () {
+      return queryInterface.addColumn('Users', 'password', Sequelize.TEXT)
+    })
   },
 
   down: function (queryInterface, Sequelize) {
-    queryInterface.removeColumn('Users', 'email')
-    queryInterface.removeColumn('Users', 'password')
+    return queryInterface.removeColumn('Users', 'email').then(function () {
+      return queryInterface.removeColumn('Users', 'password')
+    })
   }
 }