use tmux in the update script

this makes it more robust when running on an unstable connection

scripts/update_all_systems.xsh

@@ -10,6 +10,6 @@ for host in hosts:
     fqdn = "{}.2li.local".format(host)
     print(fqdn)
     print("-" * len(fqdn))
-    ssh @(fqdn) 'cd .nixos && git pull && sudo nixos-rebuild -j auto switch'
+    ssh -t @(fqdn) 'tmux new -s updates "cd ~/.nixos && git pull && sudo nixos-rebuild -j auto switch || bash;"'
     print("")
     print("")