Update Ubuntu steps

[jmerriweather]

• Change libpng3 to libpng-dev
• Add one liner

[Stratus3D]

Is there a specific version of Ubuntu that needs libpng-dev instead of libpng3? It's been a while, but I'm pretty sure the instructions in the README worked for me on Ubuntu (forget which version).

[skanderm]

Is there a specific version of Ubuntu that needs libpng-dev instead of libpng3? It's been a while, but I'm pretty sure the instructions in the README worked for me on Ubuntu (forget which version).

I needed libpng-dev for Ubuntu 18.04.2 LTS and libpng3 for Ubuntu 16.04.4 LTS.

[jmerriweather]

libpng-dev redirects to libpng12-dev on 16.04 and 14.04: https://packages.ubuntu.com/search?keywords=libpng-dev

I get the following when running on the one liner on Ubuntu 16.04:

> sudo apt-get -y install build-essential autoconf m4 libncurses5-dev libwxgtk3.0-dev libgl1-mesa-dev libglu1-mesa-dev libpng-dev libssh-dev unixodbc-dev xsltproc
Reading package lists... Done
Building dependency tree
Reading state information... Done
Note, selecting 'libpng12-dev' instead of 'libpng-dev'
E: Unable to locate package libwxgtk3.0-dev
E: Couldn't find any package by glob 'libwxgtk3.0-dev'
E: Couldn't find any package by regex 'libwxgtk3.0-dev'

[Stratus3D]

Is there another package we should be using instead of libwxgtk3.0-dev?

[jmerriweather]

libwxgtk3.0-dev actually works, I had forgotten to do an apt update

[Stratus3D]

Ok, looks good to me then. Thanks for the PR @jmerriweather !

[jmerriweather]

Glad i could contribute 😃