Fix missing include for Finder.php in redbean.inc.php

Since fffecee4e430dc4bd0b3c001d317509d4811744b, a finder is instantiated in `configureFacadeWithToolbox()` of the façade:

```
self::$finder = new RedBean_Finder( self::$toolbox );
```

For people using `redbean.inc.php`, this will throw an error because `Finder.php` was not `require()'d` in the file:

```
Fatal error: Class 'RedBean_Finder' not found in /vendor/RedBean/Facade.php on line 841
```

This fix fixes that problem.