RFR: 8278275: Initial nroff manpage generation for JDK 19

[David Holmes]

Trivial update to change the version to 19-ea, and update the single reference to the "current release".

Content changes for 19 will follow.

Thanks,
David

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Commit messages:
 - 8278275:Initial nroff manpage generation for JDK 19

Changes: https://git.openjdk.java.net/jdk/pull/6811/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6811&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278275
  Stats: 29 lines in 28 files changed: 0 ins; 0 del; 29 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6811.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6811/head:pull/6811

PR: https://git.openjdk.java.net/jdk/pull/6811