ssh: Add Newline to KnownHostsText

SSH expects a new line at the end of known_hosts file.
Without a new line the next entry goes on the same line
as the last entry in known_hosts causing errors.

nixos/modules/programs/ssh.nix

@@ -20,11 +20,11 @@ let
 
   knownHosts = map (h: getAttr h cfg.knownHosts) (attrNames cfg.knownHosts);
 
-  knownHostsText = flip (concatMapStringsSep "\n") knownHosts
+  knownHostsText = (flip (concatMapStringsSep "\n") knownHosts
     (h: assert h.hostNames != [];
       concatStringsSep "," h.hostNames + " "
       + (if h.publicKey != null then h.publicKey else readFile h.publicKeyFile)
-    );
+    )) + "\n";
 
 in
 {