test: relax the expected exception

Author: KazuCocoa

test/functional/android/android/mobile_commands_test.rb

@@ -258,7 +258,7 @@ def test_device_info
       private
 
       def assert_mobile_command_error(command, args, expected_message)
-        error = assert_raises ::Selenium::WebDriver::Error::UnknownError do
+        error = assert_raises ::Selenium::WebDriver::Error::WebDriverError do
           @driver.execute_script(command, args)
         end
         assert error.message.include? expected_message