Update the sticky topics in Competitions

If you go to the Competitions board it shows four “sticky” topics, two for SpringThing and two for IFComp 2017. I think these should be replaced with the relevant IFComp 2018 topics…

I believe I have fixed this. Let me know if it looks better.

Thanks! This topic might also be a good one to make sticky: https://intfiction.org/t/ifcomp-2018-reviews/13640/1