Changes:
- Added ffmpeg to support screen recording through Appium client, credits @Jiyvn
- Fixed documentation about port #167
- Updated Appium to version 2.11.1
- Updated Appium driver: appium-espresso-driver@2.44.1
- Updated Appium driver: appium-flutter-driver@2.8.0
- Updated Appium driver: appium-geckodriver@1.3.7
- Updated Appium driver: appium-uiautomator2-driver@3.7.1