Fixed Module::asset();
Fixed Module::asset();

Remove a frist slash.

Before fixed:

```
Module::asset('system:css/app.css');
// http://localhost:8000/\modules/system/css/app.css
```

After fixed:

```
Module::asset('system:css/app.css');
// http://localhost:8000/modules/system/css/app.css
```
nWidart/laravel-modules