A build was hanging with `UBUNTU_VERSION=20.04`
```
...
 => [base 3/5] RUN APT-GET update &&  apt-get install -y dpkg-dev git make pkg-config                                                                            73.2s
 => => # questions will narrow this down by presenting a list of cities, representing
 => => # the time zones in which they are located.
 => => #   1. Africa      4. Australia  7. Atlantic  10. Pacific  13. Etc
 => => #   2. America     5. Arctic     8. Europe    11. SystemV
 => => #   3. Antarctica  6. Asia       9. Indian    12. US
 => => # Geographic area:
...

```

Signed-off-by: Akihiro Suda <[email protected]>