Reorder course links so recent one shows at top instead of bottom

Currently, the oldest courses are shown at top (2016 Spring), we should put newer course at top (2018 Spring)

![image](https://user-images.githubusercontent.com/5621298/38636898-6a8e9c10-3d7e-11e8-8dc2-09ee8b0d6b53.png)
