Update OO exercises index (donnemartin#21)

Author: donnemartin

README.md

@@ -340,10 +340,10 @@ Check out the following links to get a better idea of what to expect:
 
 | Question | |
 |---|---|
-| Design a deck of cards to be used for blackjack | [Solution](https://github.com/donnemartin/system-design-primer/blob/master/solutions/object_oriented_design/deck_of_cards/deck_of_cards.ipynb)  |
-| Design a call center | [Solution](https://github.com/donnemartin/system-design-primer/blob/master/solutions/object_oriented_design/call_center/call_center.ipynb)  |
 | Design a hash map | [Solution](https://github.com/donnemartin/system-design-primer/blob/master/solutions/object_oriented_design/hash_table/hash_map.ipynb)  |
 | Design a least recently used cache | [Solution](https://github.com/donnemartin/system-design-primer/blob/master/solutions/object_oriented_design/lru_cache/lru_cache.ipynb)  |
+| Design a call center | [Solution](https://github.com/donnemartin/system-design-primer/blob/master/solutions/object_oriented_design/call_center/call_center.ipynb)  |
+| Design a deck of cards | [Solution](https://github.com/donnemartin/system-design-primer/blob/master/solutions/object_oriented_design/deck_of_cards/deck_of_cards.ipynb)  |
 | Design a parking lot | [Solution](https://github.com/donnemartin/system-design-primer/blob/master/solutions/object_oriented_design/parking_lot/parking_lot.ipynb)  |
 | Design a chat server | [Solution](https://github.com/donnemartin/system-design-primer/blob/master/solutions/object_oriented_design/online_chat/online_chat.ipynb)  |
 | Design a circular array | [Contribute](#contributing)  |