Fix ModuleNotFoundError
```bash
$ mtk --help
Traceback (most recent call last):
File "/usr/bin/mtk", line 5, in <module>
from mtk import main
ModuleNotFoundError: No module named 'mtk'
```
```bash
$ mtk_gui
Traceback (most recent call last):
File "/usr/bin/mtk_gui", line 5, in <module>
from mtk_gui import main
ModuleNotFoundError: No module named 'mtk_gui'
```
```bash
$ stage2 --help
Traceback (most recent call last):
File "/usr/bin/stage2", line 5, in <module>
from stage2 import main
ModuleNotFoundError: No module named 'stage2'
```