RFR: JDK-8309686: inconsistent URL for https://www.unicode.org/reports/tr35

[Jonathan Gibbons]

Please review a trivial docs change to fix a URL in a `@spec` tag consistent with equivalent URLs in other tags.
(Consistency will be required when the External Specifications page is enabled.)

-------------

Commit messages:
 - JDK-8309686: inconsistent URL for https://www.unicode.org/reports/tr35

Changes: https://git.openjdk.org/jdk/pull/14384/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14384&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309686
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14384.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14384/head:pull/14384

PR: https://git.openjdk.org/jdk/pull/14384