Wrong depends on Debian package

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## Describe the problem
Debian packages depends on `cron` when it should be `cron-daemon`

## Steps to reproduce
Install `systemd-cron` to replace `cron`

## Expected behavior

## System Information
Distribution and version:
Debian 9.8

### do-agent information:
Paste the entire output

`/opt/digitalocean/bin/do-agent --version`:
Not Found

_Ubuntu, Debian_

`apt-cache policy do-agent`:
```
root@gitlab:~# apt-cache policy do-agent
do-agent:
Installed: (none)
Candidate: 2.1.3
Version table:
2.1.3 500
500 https://repos.insights.digitalocean.com/apt/do-agent main/main amd64 Packages
2.0.2 500
500 https://repos.insights.digitalocean.com/apt/do-agent main/main amd64 Packages
2.0.1 500
500 https://repos.insights.digitalocean.com/apt/do-agent main/main amd64 Packages
2.0.0 500
500 https://repos.insights.digitalocean.com/apt/do-agent main/main amd64 Packages
1.1.3 500
500 https://repos.insights.digitalocean.com/apt/do-agent main/main amd64 Packages
```