Adding PPA's fails if not being run as root

Previously

```
Stderr from the command:

            Error: must run as root
 failed
            E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied)
            E: Unable to lock directory /var/lib/apt/lists/
            E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied)
            E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?
 failed
```

relevant dep
```ruby
dep "tmux.managed" do
  requires "ppa".with("ppa:pi-rho/dev")
  installs "tmux"
  provides "tmux"
end
```