ios-6.2.0

• Added support for App Open Ad (https://developers.google.com/admob/ios/app-open)
• Reset TC string if last updated date was more than 13 months ago (https://developers.google.com/admob/ios/privacy/gdpr#troubleshooting)
• Renamed Interstitial and Rewarded Video event names:
  -- adloaded becomes didReceiveAd
  -- adfailedtoload becomes didFailToReceiveAd
  -- adrewarded becomes didRewardUser
• Added didRecordImpression and didRecordClick events to all ad types
• Added didFailToShowAd event to Open App ad type
• Removed deprecated didPresentScreen event
• Updated documentation and iOS example