doc: fix missing parenthesis with client examples (#1046)

objects/client.c

@@ -61,20 +61,20 @@
  *
  *    client.connect_signal("manage", function(c)
  *        -- do something
- *    end
+ *    end)
  *
  * To be notified a property changed in a client, use:
  *
  *    client.connect_signal("property::name", function(c)
  *        -- do something
- *    end
+ *    end)
  *
  * To be notified when a property change for a specific client (assuming it is
  * stored in the variable `c`), use:
  *
  *    c:connect_signal("property::name", function()
  *        -- do something
- *    end
+ *    end)
  *
  * To get all the clients for a screen, use either `screen.clients` or
  * `screen.tiled_clients`