[FLINK-10207] Bump checkstyle-plugin to 8.9

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.7.0
• Fix Version/s: 1.7.0
• Component/s: Build System
• Labels: pull-request-available
• Assignee: Chesnay Schepler
• Reporter: Chesnay Schepler
• Created: 24/Aug/18 08:48
• Updated: 31/Aug/18 10:24
• Resolved: 29/Aug/18 20:17

Description

Our current checkstyle version (8.4) is incompatible with java 9, the earliest version to work properly is 8.9.

Issue Links

• supercedes: FLINK-9825 Upgrade checkstyle version to 8.6
• links to: GitHub Pull Request #6618