Download correct geckdriver file on Apple Silicon

Geckodriver splits its Mac OS files into 2 versions (macos.tar.gz and macos-aarch64.tar.gz), and webdriver doesn't work properly if `macos.tar.gz` is used on Apple Sillicon platform.
Geckodriver releases: https://github.com/mozilla/geckodriver/releases

lib/webdrivers/geckodriver.rb

@@ -51,7 +51,7 @@ def platform_ext
         when 'linux'
           "linux#{System.bitsize}.tar.gz"
         when 'mac'
-          'macos.tar.gz'
+          System.apple_m1_architecture? ? 'macos-aarch64.tar.gz' : 'macos.tar.gz'
         when 'win'
           "win#{System.bitsize}.zip"
         end