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

spec/webdrivers/geckodriver_spec.rb

@@ -92,6 +92,40 @@
       msg = /Net::HTTPServerException: 404 "Not Found"/
       expect { geckodriver.update }.to raise_error(StandardError, msg)
     end
+
+    context 'when platform is Apple Sillicon' do
+      it 'downloads aarch64 binary' do
+        allow(Webdrivers::System).to receive(:platform).and_return('mac')
+        allow(Webdrivers::System).to receive(:apple_m1_architecture?).and_return(true)
+        base = 'https://github.com/mozilla/geckodriver/releases/download'
+        binary = 'geckodriver-v0.31.0-macos-aarch64.tar.gz'
+        url = "#{base}/v0.31.0/#{binary}"
+
+        allow(Webdrivers::System).to receive(:download).with(url, geckodriver.driver_path)
+
+        geckodriver.required_version = '0.31.0'
+        geckodriver.update
+
+        expect(Webdrivers::System).to have_received(:download).with(url, geckodriver.driver_path)
+      end
+    end
+
+    context 'when platform isn\'t Apple Sillicon' do
+      it 'downloads default binary' do
+        allow(Webdrivers::System).to receive(:platform).and_return('mac')
+        allow(Webdrivers::System).to receive(:apple_m1_architecture?).and_return(false)
+        base = 'https://github.com/mozilla/geckodriver/releases/download'
+        binary = 'geckodriver-v0.31.0-macos.tar.gz'
+        url = "#{base}/v0.31.0/#{binary}"
+
+        allow(Webdrivers::System).to receive(:download).with(url, geckodriver.driver_path)
+
+        geckodriver.required_version = '0.31.0'
+        geckodriver.update
+
+        expect(Webdrivers::System).to have_received(:download).with(url, geckodriver.driver_path)
+      end
+    end
   end
 
   describe '#current_version' do