fixed regex as it wasn't finding any matches

using the following `manifest.json` 

```json
{
  "name": "TestApp",
  "author": {
    "name": "Bulkan Evcimen",
    "email": "bulkan@gmail.com"
  },
  "defaultLocale": "en",
  "private": true,
  "singleInstall": false,
  "location": ["user_sidebar"],
  "version": "1.0.0",
  "frameworkVersion": "0.5",
  "parameters": [
    {
      "name": "backend",
      "type": "text",
      "required": true,
      "default": "https://example.com:3000"
    }
}
```

running `zat server --path /testapp` will zat will prompt for user input to set the _backend_ setting. All user input is treated as invalid. 

This commit fixed this issue.