fixed empty echo for laravel 4

Author: concentriccircles

src/views/render_activity.blade.php

@@ -13,6 +13,6 @@
         @endif
     @endif
 @else
-    {{  }}
+    {{ '' }}
     Log::warning('The activity could not be rendered, the following field/refs could not be enriched:', $activity->getNotEnrichedData());
 @endif