Fixing error with compatibility with Interface

I installed this module and got an error. Here is a fix.

```
Fatal error: Declaration of Drupal\entity_embed\Plugin\Filter\EntityEmbedFilter::process() must be compatible with Drupal\filter\Plugin\FilterInterface::process($text, $langcode, $cache, $cache_id) in /Users/persch/Sites/d8_dev/docroot/modules/entity_embed/src/Plugin/Filter/EntityEmbedFilter.php on line 34
```


![screen shot 2014-06-03 at 4 03 27 pm](https://cloud.githubusercontent.com/assets/211029/3166736/2f47973a-eb64-11e3-9c0d-fbf3b24dd601.png)