fix(backup): Ensure the backup is up-to-date

refs: TryGhost/Toolbox#334
refs: #468

- if the backup command is run multiple times, and the latter runs fail to export, the backup files would be old
- this ensures that the backup files all belong together
- also renames backup to content

lib/tasks/backup.js

@@ -8,9 +8,12 @@ const {ProcessError} = require('../errors');
 const {exportTask} = require('./import');
 
 module.exports = async function (ui, instance) {
+    const datetime = require('moment')().format('YYYY-MM-DD-HH-mm-ss');
+    const backupSuffix = `from-v${instance.version}-on-${datetime}`;
+
     // First we need to export the content into a JSON file & members into a CSV file
-    const contentExportPath = 'data/backup.json';
-    const membersExportPath = 'data/members.csv';
+    const contentExportPath = `data/content-${backupSuffix}.json`;
+    const membersExportPath = `data/members-${backupSuffix}.csv`;
 
     await exportTask(ui, instance, path.join(instance.dir, 'content/', contentExportPath), path.join(instance.dir, 'content/', membersExportPath));
 
@@ -34,8 +37,7 @@ module.exports = async function (ui, instance) {
     }
 
     // Finally we zip everything up into a nice little package
-    const datetime = require('moment')().format('YYYY-MM-DD-HH-mm-ss');
-    const zipPath = path.join(process.cwd(), `backup-from-v${instance.version}-on-${datetime}.zip`);
+    const zipPath = path.join(process.cwd(), `backup-${backupSuffix}.zip`);
 
     try {
         execa.shellSync(`zip -r ${zipPath} ${contentExportPath} ${membersExportPath} files/ images/ media/ settings/ themes/`, {