detect if nginx is already installed

[jgallen23]

Is there any way to detect if nginx is already installed before doing the apt-get update and apt-get install nginx? I'm fairly new to dokku, so I'm not sure if a completely new docker container gets started on every push or it uses the existing one. I'm guessing if it's a new docker container, there's no way around this, but just checking.

It uses a new docker container each time (which doesn't have nginx installed), but the cache directory could be used to cache the .deb for a day or so. You'd miss out on any updates that happened to be pushed out during that period (e.g. security updates) but you'd get a nice speed boost as apt wouldn't have to update and download the .deb again for the app.

[jgallen23]

pull request submitted #9