Python: change import order

`pylint` is complaining about the import order:

```
zip.py:5:0: C0411: standard import "from enum import Enum" should be placed before "import kaitaistruct" (wrong-import-order)
zip.py:6:0: C0411: standard import "import collections" should be placed before "import kaitaistruct" (wrong-import-order)
```