Fixes missing Elastica\Script use in Elastica\Facet\Terms::setScript()

After merging master got this error in test
```sh
1) Elastica\Test\Facet\TermsTest::testFacetScript
PHPUnit_Framework_Exception: PHP Fatal error:  Class 'Elastica\Facet\Script' not found in /home/munkie/Projects/Elastica/lib/Elastica/Facet/Terms.php on line 45
```
Elastica\Facet\Terms::setScript() method was introduced in PR #324