Python 3.8 compatibility

Python 3.8 compatibility

• Set pip minimum version to be 19.3.1 for Python 3.8 compatibility
• Set default Geckodriver (Firefox WebDriver) to version 0.26.0
• Update dependency requirements of dependencies for better compatibility
  ** atomicwrites>=1.3.0
  ** portalocker>=1.5.1
  ** cryptography>=2.8
  ** asn1crypto>=1.2.0