Comment 0 for bug 1820055

I'm migrating a snap with a legacy snapcraft syntax to the new one with bases, however the previous command to launch the application:

```yaml
    command: >
      bin/zenity
        --info
        --ok-label='Got it'
        --title='My Awesome App'
        --text='This is a demonstrative application for Snapcrafters Template Plus.\nIt indicates that the snapped application has been launched properly.'
        --window-icon="${SNAP}"/snap/gui/my-awesome-app.png
        --width=600
```

no longer work and causes the following Snapcraft error message:

```
Failed to generate snap metadata: The specified command 'bin/zenity\n --info\n --ok-label=\'Got it\'\n --title=\'My Awesome App\'\n --text=\'This is a demonstrative application for Snapcrafters Template Plus.\\nIt indicates that the snapped application has been launched properly.\'\n --window-icon="${SNAP}"/snap/gui/my-awesome-app.png\n --width=600\n' defined in the app 'my-app-name' does not match the pattern expected by snapd.
The command must consist only of alphanumeric characters, spaces, and the following special characters: / . _ # : $ -
```

although this problem can be easily workarounded by using a launcher we probably should reconsider whether we should impose a restriction to this property as it can be any arbitrary string.