Fix decoder bug

This patch fixes a bug that existed in the decoder for the translation files. The namespace was cleared for all nested keys expect the first one.
With the bug a JSON file like this :

{
  "a": {
    "b": "hello",
    "c": "bye"
  }
}

was decoded into Dict.fromList [("a.b","Hello"),("c","bye")] instead of Dict.fromList [("a.b","Hello"),("b.c","bye")].

Decoding now works properly for all nested keys.