vagrant: Don't patch salt provisioner's shebang

The script is intended to run on remote systems, not on the local
system. The shebang **has** to work where nix and the current store does
not exist.

pkgs/development/tools/vagrant/default.nix

@@ -84,6 +84,13 @@ in buildRubyGem rec {
     fi
   '';
 
+  # `patchShebangsAuto` patches this one script which is intended to run
+  # on foreign systems.
+  postFixup = ''
+    sed -i -e '1c#!/bin/sh -' \
+      $out/lib/ruby/gems/*/gems/vagrant-*/plugins/provisioners/salt/bootstrap-salt.sh
+  '';
+
   passthru = {
     inherit ruby deps;
   };