updated madebysofa url and changed "if success != 0" to "unless success"

sample-macruby/Scripts/gcd/sleeping_barber.rb

@@ -1,14 +1,14 @@
 # A GCD-based implementation of the sleeping barber problem:
 #   http://en.wikipedia.org/wiki/Sleeping_barber_problem
-#   http://www.madebysofa.com/#blog/the_sleeping_barber
+#   http://www.madebysofa.com/archive/blog/the-sleeping-barber/
 
 waiting_chairs = Dispatch::Queue.new('com.apple.waiting_chairs')
 semaphore = Dispatch::Semaphore.new(3)
 index = -1
 while true
   index += 1
   success = semaphore.wait(Dispatch::TIME_NOW)
-  if success != 0
+  unless success
     puts "Customer turned away #{index}"
     next
   end