test failure, 1.0.3.2, header order Access-Control-Allow-Headers, guix i386

snap-core version 1.0.3.2 has failed tests on guix, i386. I don't see relevant changes in the code since then, so I'm guess this might still be relevant:

```
Header "Access-Control-Allow-Headers"
expected: Just "X-STUFF, Content-Type"
 but got: Just "Content-Type, X-STUFF"
```

Full log here: http://ci.guix.gnu.org/log/cz6rhbxwz3plvrvwn6pkh4jigasbcq2y-ghc-snap-core-1.0.3.2