Fixed typo in the ServiceProviderInterface interface PHPDoc block.

src/Silex/ServiceProviderInterface.php

@@ -31,7 +31,7 @@ interface ServiceProviderInterface
     /**
      * Bootstraps the application.
      *
-     * This method is called after all services are registers
+     * This method is called after all services are registered
      * and should be used for "dynamic" configuration (whenever
      * a service must be requested).
      */