Remove github.com/Unknown/cae/zip dependency

This package seems to be useless (and implementation broken).

$ go build -o tutorial/bin/basic_window tutorial/basic_window.go
# github.com/miketheprogrammer/go-thrust/spawn
spawn/helper_darwin.go:67: undefined: "github.com/Unknwon/cae/zip".ExtractTo

Signed-off-by: Stéphane Depierrepont <toorop@toorop.fr>