Update fourch.py

Updates the urls to the new cookie-less domain as requested on the 4chan API documentation.
https://github.com/4chan/4chan-API

api.4chan.org --> a.4cdn.org
images.4chan.org --> i.4cdn.org
0.thumbs.4chan.org --> t.4cdn.org
Merge pull request #1 from feblehober123/patch-1

Update fourch.py