To those who still have the problem connecting to steemworld:
I had the same problem on my machine and discovered I could connect from my phone. So I made a hotspot from my phone and tried to connect from my pc -> problem solved.
I suppose it's a local DNS cache problem. I cleared my PC DNS cache but that didn't solved the problem. Next thing I'll try is to clear the cache from my router...

EDIT: problem is now completely solved by rebooting my router!