py-lexicon: updated to 3.4.3

3.4.3:

Modified
Improve versions constraints by declaring latest major versions known to work with Lexicon

3.4.2:

Modified
Relax versions constraints on Lexicon dependencies until there is a real need.

3.4.1:

Added
Add the Njalla provider

3.4.0:

Added
Use poetry to manage dependencies, build and package Lexicon.
Add integration tests for Mac OS X

Changed
The beautifulsoup4 dependency has been integrated to the core ones for generic purpose. As a consequence henet, easyname and gratisdns providers do not have optional dependencies anymore.
Update Docker image to use Python 3.8, and install Lexicon with full extras.

Removed
Remove support for Python 2.7.
Remove support for Python 3.5.
Remove the extra security from requests dependency which does not make sense anymore on recent versions of Python.

(adam)