shell.nix: add libxcrypt (needed for some python junk)

Change-Id: Ie094aa06669c82018708534eea58a161f89f8742
Reviewed-on: https://gerrit.hackerspace.pl/c/hscloud/+/1492
Reviewed-by: q3k <q3k@hackerspace.pl>
diff --git a/shell.nix b/shell.nix
index f20cbb0..bf9f8ae 100644
--- a/shell.nix
+++ b/shell.nix
@@ -61,6 +61,7 @@
     nix
     vim
     openssh
+    libxcrypt
   ];
   multiPkgs = pkgs: [
     (pkgs.runCommand "protocols" {}