destroyAllNow also has a callback

lib/index.js

@@ -25,13 +25,14 @@ PG.prototype.end = function() {
     var pool = self.pools.all[key];
     delete self.pools.all[key];
     pool.drain(function() {
-      pool.destroyAllNow();
+      pool.destroyAllNow(function() {
         count--;
         if(count === 0) {
           self.emit('ended');
         }        
       });
     });
+  });
 };