Build.sh - Add cython3 requirement, fix typo in "exit"

[bartleskeet]

The build.sh file failed when running the update command on my machine, as I didn't have cython3 installed. Where it's already calling "apt-get", I think it'd make sense to add this to the packages that are installed. Also brought up here: #98 (comment)

There's also a typo in the exit command ("ecit"):

torghost/build.sh

Line 27 in 375bc62

ecit 1

Thanks for the neat tool!

[bartleskeet]

PR #108