#432 proposing use of python3 metapackage on Debian-alike systems ins…

[emmcauley]

…tead of locking to specific version that requires a PPA be used

Description //

Changes related to pull request #32 / issue #31 -- there didn't seem to be a specific reason documented to lock specifically to Python 3.6 or pull in a custom PPA. The changes I am proposing in this pull request let the Ubuntu/Debian "python3" meta-package select the supported version of Python3 for that system and removes the deadsnakes-ppa line.

Affected Dependencies

List any dependencies that are required for this change. // None

How has this been tested?

• Describe the tests that you ran to verify your changes // -I did not run any tests on these changes.
• Provide instructions so we can reproduce.
• List any relevant details for your test configuration.

Checklist

• [X ] I have followed the Contribution Guidelines and Code of Conduct
• [X ] I have commented my code following the OpenMined Styleguide
• [X] I have labeled this PR with the relevant Type labels
• [ ] My changes are covered by tests