fix sf3 depreciated addViolationAt() method

cfr vendor/symfony/symfony/UPGRADE-3.0.md:1719

Entity/AccompanyingPeriod.php

@@ -224,9 +224,9 @@ class AccompanyingPeriod
         }
         
         if (! $this->isClosingAfterOpening()) {
-            $context->addViolationAt('dateClosing', 
-                'The date of closing is before the date of opening',
-                array(), null);
+            $context->buildViolation('The date of closing is before the date of opening')
+                ->atPath('dateClosing')
+                ->addViolation();
         }
     }