Use ISO 8601 date for FCM

[svenseeberg]

Your checklist for this pull request

• Check if patches need to be applied.
  • Patch 0001 - WPML
  • Patch 0002 - Broken Link Checker
  • Patch 0003 - CMS Tree View
  • Patch 0004 - Sitepress
• Make sure you are requesting to pull a topic/feature/bugfix branch (right side). Don't request your master!
• Make sure you are making a pull request against the develop branch (left side). Also you should start your branch off develop.
• Check the commit's or even all commits' message styles matches your requested structure.
• Check your code additions will fail neither code linting checks nor unit test.