get started: driver version numbers

[kremalicious]

In theory™ and in an ideal world™, the whole drivers section would be sourced by 1 response from github-projects, populated with js only.

For now, the section is constructed on Jekyll level during site build sourced from the drivers.yml data file. So version numbers need to be updated manually, like they did in the middle ages.

As a first start, get and display only the version numbers based on a response from github-projects.

Blocked by bigchaindb/github-projects#7