Fixed Admin-X path variable

refs https://github.com/TryGhost/DevOps/issues/80

- I'd previously used the wrong one

ghost/admin/lib/asset-delivery/index.js

@@ -48,7 +48,7 @@ module.exports = {
         const adminXSettingsPath = '../../apps/admin-x-settings/dist';
         const assetsAdminXPath = `${assetsOut}/assets/libs/admin-x-settings`;
 
-        if (fs.existsSync(assetsAdminXPath)) {
+        if (fs.existsSync(adminXSettingsPath)) {
             if (this.env === 'production') {
                 fs.copySync(adminXSettingsPath, assetsAdminXPath, {overwrite: true, dereference: true});
             } else {