gitlab: Limit node memory consumption to 2048MB

Hydra fails to build the assets on i686 - it runs out of memory. If we
limit the max consumption to 2048MB the assets still build, and will
hopefully also build on hydra.

pkgs/applications/version-management/gitlab/default.nix

@@ -76,7 +76,7 @@ let
 
       bundle exec rake gettext:po_to_json RAILS_ENV=production NODE_ENV=production
       bundle exec rake rake:assets:precompile RAILS_ENV=production NODE_ENV=production
-      bundle exec rake webpack:compile RAILS_ENV=production NODE_ENV=production NODE_OPTIONS="--max_old_space_size=4096"
+      bundle exec rake webpack:compile RAILS_ENV=production NODE_ENV=production NODE_OPTIONS="--max_old_space_size=2048"
       bundle exec rake gitlab:assets:fix_urls RAILS_ENV=production NODE_ENV=production
 
       runHook postBuild