Install ca-certificates via preseed tasksel

Resolves: #4

preseed.cfg

@@ -321,10 +321,10 @@ d-i base-installer/kernel/image string linux-image-amd64
 tasksel tasksel/first multiselect ssh-server
 
 # Individual additional packages to install
-#d-i pkgsel/include string openssh-server build-essential
+d-i pkgsel/include string ca-certificates
 # Whether to upgrade packages after debootstrap.
 # Allowed values: none, safe-upgrade, full-upgrade
-#d-i pkgsel/upgrade select none
+d-i pkgsel/upgrade select full-upgrade
 
 # Some versions of the installer can report back on what software you have
 # installed, and what software you use. The default is not to report back,