nixos/ssh: fix example

nixos/modules/programs/ssh.nix

···
           [
             {
               hostNames = [ "myhost" "myhost.mydomain.com" "10.10.1.4" ];
-              publicKeyFile = "./pubkeys/myhost_ssh_host_dsa_key.pub";
+              publicKeyFile = ./pubkeys/myhost_ssh_host_dsa_key.pub;
             }
             {
               hostNames = [ "myhost2" ];
-              publicKeyFile = "./pubkeys/myhost2_ssh_host_dsa_key.pub";
+              publicKeyFile = ./pubkeys/myhost2_ssh_host_dsa_key.pub;
             }
           ]
         '';