update readme

Author: edk

README.md

@@ -3,7 +3,8 @@ Resque-round-robin
 
 A plugin for Resque that implements round-robin behavior for workers.
 
-resque-dynamic-queues is a pre-requisite, as is Resque 1.19
+resque-dynamic-queues is a pre-requisite, as is Resque 1.19 or higher
+(now tested up to 1.21)
 
 The standard behavior for Resque workers is to pull a job off a queue,
 and continue until the queue is empty.  Once empty, the worker moves