Fix double colons typos in code (#567)

pep-0342.txt

@@ -420,7 +420,7 @@ Examples
                 destination.send(page)
 
     @consumer
-    def jpeg_writer(dirname)::
+    def jpeg_writer(dirname):
         fileno = 1
         while True:
             filename = os.path.join(dirname,"page%04d.jpg" % fileno)
@@ -475,7 +475,7 @@ Examples
             result = None
             self.running = True
             try:
-                while self.running and self.queue::
+                while self.running and self.queue:
                    func = self.queue.popleft()
                    result = func()
                 return result