CI: drop the 'python 2' builds from Travis

[vince-fugnitto]

Feature Description:

At the moment, we are performing build stages during continuous integration (Travis) with Python 2 which is EOL.
Alternatively, can we drop it in favor of building solely with Python 3, or is there a reason we want to build/test with Python 2?

The build is now possible with Python 3 thanks to the updates to node-gyp: #8216