fix(backup): swap to using @tryghost/zip

refs: TryGhost/Toolbox#334
refs: #468

- zip is meant to be installed on ubuntu 18 but for some reason on DO it is not
- use our JS lib instead, as that will work on any platform, although it may have issues with scaling

lib/tasks/backup.js

@@ -1,7 +1,7 @@
 const path = require('path');
+const zip = require('@tryghost/zip');
 
 const debug = require('debug')('ghost-cli:backup');
-const execa = require('execa');
 const fs = require('fs-extra');
 
 const ghostUser = require('../utils/use-ghost-user');
@@ -74,13 +74,8 @@ module.exports = async function (ui, instance) {
     const zipPath = path.join(process.cwd(), `backup-${backupSuffix}.zip`);
 
     try {
-        execa.shellSync(`zip -r ${zipPath} data/${membersExportFile} data/${membersExportFile} files/ images/ media/ settings/ themes/`, {
-            cwd: path.join(instance.dir, 'content/')
-        });
+        await zip.compress(path.join(instance.dir, 'content/'), zipPath, {glob: `{data/${contentExportFile},data/${membersExportFile},files/**,images/**,media/**,settings/**,themes/**}`});
     } catch (err) {
-        if (err.stderr.match(/zip.*?not found/)) {
-            err.message = `Package zip was not found. Please install by running \`sudo apt install zip\`. \n${err.message}`;
-        }
         throw new ProcessError(err);
     }
 

package.json

@@ -43,6 +43,7 @@
   },
   "preferGlobal": true,
   "dependencies": {
+    "@tryghost/zip": "^1.1.25",
     "abbrev": "1.1.1",
     "adm-zip": "0.5.9",
     "bluebird": "3.7.2",