@haxxim Looks like you (temporarily) have a slow connection or another problem with Internet. So eopkg can't download the whole file.
The good choice is to wait some time, until the connection turns normal.
Otherwise, if you can't wait, download the file by hand:
cd /var/cache/eopkg/packages
sudo wget https://mirrors.rit.edu/solus/packages/shannon/libw/libwebkit-gtk/libwebkit-gtk-2.26.1-63-1-x86_64.eopkg
After that, run your eopkg commands again. eopkg will find the package in the cache and won't try to fetch it from the mirror.