download_libs.sh doesn't properly download alternate versions

I believe I've found a bug in the download_libs.sh where if a VER is supplied (such as 0.10.1 or 0.11.0), the download fails. It looks like the script's logic doesn't match the URL structure of the CI filestore it downloads from (http://ci.openframeworks.cc/libs/).

An example URL is generated here:

https://github.com/openframeworks/openFrameworks/blob/28d3b492dd289895d8b2b6b67860e1dbd966eb4f/scripts/dev/download_libs.sh#L190

Which is then used here:

https://github.com/openframeworks/openFrameworks/blob/28d3b492dd289895d8b2b6b67860e1dbd966eb4f/scripts/dev/download_libs.sh#L31-L34

The logic works for a default VER of master, but doesn't work for named semantic versions (ex 0.10.1) as their URLs look like http://ci.openframeworks.cc/libs/0.10.1/openFrameworksLibs_master_linux64gcc6.tar.bz2.

A solution might catch a semver VER and direct to the correct file or add an additional variable for named branches.

I found then when attempting to implement a continuous integration build system where openFrameworks is tagged to a specific version.

Thanks!