Lexicon v3.4.0

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.