Don't block releases on nixos.tests.gnome3.i686-linux

http://hydra.nixos.org/build/26702440

Issue #10353.

Changed files
+1 -1
nixos
+1 -1
nixos/release-combined.nix
···
(all nixos.tests.chromium)
(all nixos.tests.firefox)
(all nixos.tests.firewall)
-
(all nixos.tests.gnome3)
+
nixos.tests.gnome3.x86_64-linux # FIXME: i686-linux
(all nixos.tests.installer.lvm)
(all nixos.tests.installer.luksroot)
(all nixos.tests.installer.separateBoot)