use Resque.encode instead of to_s for stringifying arguments

lib/resque/plugins/lock.rb

@@ -53,7 +53,7 @@ def lock_timeout
       # passed the same arguments as `perform`, that is, your job's
       # payload.
       def lock(*args)
-        "lock:#{name}-#{args.to_s}"
+        "lock:#{name}-#{Resque.encode(args)}"
       end
 
       # See the documentation for SETNX http://redis.io/commands/setnx for an