RFR: CODETOOLS-7903025: Update version to 6.2

[Jonathan Gibbons]

Update the version number, now that 6.1 has been promoted.  The next version will (likely) be 6.2

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Commit messages:
 - CODETOOLS-7903025: Update version to 6.2

Changes: https://git.openjdk.java.net/jtreg/pull/27/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=27&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903025
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/27.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/27/head:pull/27

PR: https://git.openjdk.java.net/jtreg/pull/27