Ignore errors on 5.3 as well

src/Monolog/Formatter/LineFormatter.php

@@ -97,6 +97,6 @@ class LineFormatter extends NormalizerFormatter
             return $this->toJson($data, true);
         }
 
-        return str_replace('\\/', '/', json_encode($data));
+        return str_replace('\\/', '/', @json_encode($data));
     }
 }