travis: refine NixOS options check

Looks like --show-trace wasn't as useful as I'd hoped.  Also, because checking
nixos options is cheaper than checking the tarball, it makes sense to check the
options first to fail faster.

maintainers/scripts/travis-nox-review-pr.sh

@@ -23,12 +23,12 @@ elif [[ $1 == nox ]]; then
 elif [[ $1 == build ]]; then
     source $HOME/.nix-profile/etc/profile.d/nix.sh
 
+    echo "=== Checking NixOS options"
+    nix-build nixos/release.nix -A options
+
     echo "=== Checking tarball creation"
     nix-build pkgs/top-level/release.nix -A tarball
 
-    echo "=== Checking NixOS options"
-    nix-build --show-trace nixos/release.nix -A options
-
     if [[ $TRAVIS_PULL_REQUEST == false ]]; then
         echo "=== Not a pull request"
     else