version 1.39.3

Changes

• [slack-api-client] #1316 Fix #1314 files.upload v2 method does not upload multiple files with full metadata - Thanks @oppokui @seratch

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• All issues/pull requests: https://github.com/slackapi/java-slack-sdk/milestone/99?closed=1
• All changes: v1.39.2...v1.39.3