jetty: 12.0.7 -> 12.0.8

https://github.com/jetty/jetty.project/releases/tag/jetty-12.0.8

pkgs/servers/http/jetty/12.x.nix

···
 import ./common.nix {
-  version = "12.0.7";
-  hash = "sha256-n85MgRRWCaa7+KvGH1QyiQ03TFoAw7N2jPCJbmuGZNg=";
+  version = "12.0.8";
+  hash = "sha256-lmlt2bjomXl7UWu3FDUBSLGv0oyXV/8kPhRCtfSUW7w=";
 }