Feature: add WDM_SSL_VERIFY env property

[aleksandr-kotlyar]

Details: added WDM_SSL_VERIFY env property to disable requests ssl verification (feature to fix issues #219, #226)

• covered with tests
• updated CHANGELOG
• updated README

Closes #219
Closes #226

[codecov-commenter]

Codecov Report

Merging #253 (4b8e6eb) into master (7e92270) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #253      +/-   ##
==========================================
+ Coverage   88.17%   88.19%   +0.02%     
==========================================
  Files          11       11              
  Lines         465      466       +1     
  Branches       52       52              
==========================================
+ Hits          410      411       +1     
  Misses         37       37              
  Partials       18       18              

Impacted Files	Coverage Δ
webdriver_manager/driver.py	95.83% <100.00%> (+0.02%)	⬆️
webdriver_manager/manager.py	100.00% <100.00%> (ø)
webdriver_manager/utils.py	74.07% <100.00%> (ø)

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