nixos/fail2ban: don't use types.string (it's deprecated)

I'm not really sure which one of types.lines or types.str that fit
better, but I'm going for types.lines because it behaves more like the
current type (i.e. have the ability to merge).

nixos/modules/services/security/fail2ban.nix

@@ -40,7 +40,7 @@ in
             socket    = /run/fail2ban/fail2ban.sock
             pidfile   = /run/fail2ban/fail2ban.pid
           '';
-        type = types.string;
+        type = types.lines;
         description =
           ''
             The contents of Fail2ban's main configuration file.  It's
@@ -64,7 +64,7 @@ in
                 maxretry = 5
               '';
           };
-        type = types.attrsOf types.string;
+        type = types.attrsOf types.lines;
         description =
           ''
             The configuration of each Fail2ban “jail”.  A jail