Add guard condition for packages to fix error on Debian
Add guard condition for packages to fix error on Debian

This condition is intended for Ubuntu.

- 323424d0f3743f1ae9c3961b201b53b6a4935fa6
- 80d3d37d6bd923561f080070622ff3729f7949d1

I've got following error on Debian stretch.

```
ERROR :           stdout | パッケージリストを読み込んでいます...
ERROR :           stdout | 依存関係ツリーを作成しています...
ERROR :           stdout | 状態情報を読み取っています...
ERROR :           stderr | E: パッケージ libgdbm5 が見つかりません
ERROR :           Command `DEBIAN_FRONTEND='noninteractive' apt-get -y -o Dpkg::Options::='--force-confdef' -o Dpkg::Options::='--force-confold'  install libgdbm5` failed. (exit status: 100)
ERROR :         package[libgdbm5] Failed.
```

In Debian stretch, the `node[:platform_version]` is `"9.5"` and it's greater than `"18.04"`.

```
$ mruby -e 'p "9.5" >= "18.04"'
true
```

But libgdbm5 is not in Debian stretch's repository.

k0kubun/itamae-plugin-recipe-rbenv