[FLINK-20906] Update copyright year to 2021 for NOTICE files

• Type: Improvement
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Fix Version/s: 1.10.3, 1.11.4, 1.12.1, 1.13.0
• Component/s: Release System
• Labels: pull-request-available
• Assignee: Xintong Song
• Reporter: Xintong Song
• Created: 09/Jan/21 12:20
• Updated: 28/May/21 07:08
• Resolved: 15/Jan/21 08:42

Issue Links

• links to: GitHub Pull Request #14598
• links to: GitHub Pull Request #14599
• links to: GitHub Pull Request #14600
• links to: GitHub Pull Request #14661
• links to: PR for flink-shaded