Replaced Promise.each() with .all() in models/base/bookshelf (TryGhos…

…t#15509)

refs: TryGhost#14882

- Removing bluebird specific methods in favour of native promises so we can remove the bluebird dependency.

Co-authored-by: Carol-Barno <cbarno@innovexsolutions.co.ke>
Co-authored-by: Hannah Wolfe <github.erisds@gmail.com>

ghost/core/core/server/models/base/bookshelf.js

@@ -2,7 +2,6 @@ const _ = require('lodash');
 const bookshelf = require('bookshelf');
 const ObjectId = require('bson-objectid').default;
 const plugins = require('@tryghost/bookshelf-plugins');
-const Promise = require('bluebird');
 
 const db = require('../../data/db');
 
@@ -84,13 +83,13 @@ ghostBookshelf.plugin('bookshelf-relations', {
                     return Promise.resolve();
                 }
 
-                return Promise.each(targets.models, function (target, index) {
+                return Promise.all(targets.models.map((target, index) => {
                     queryOptions.query.where[existing.relatedData.otherKey] = target.id;
 
                     return existing.updatePivot({
                         sort_order: index
                     }, _.extend({}, options, queryOptions));
-                });
+                }));
             },
             beforeRelationCreation: function onCreatingRelation(model, data) {
                 data.id = ObjectId().toHexString();