RFR: 8301299: Wrong class spec on sun.security.util.Pem

[Weijun Wang]

A trivial doc-only change.

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Commit messages:
 - the fix

Changes: https://git.openjdk.org/jdk/pull/12373/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12373&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301299
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12373.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12373/head:pull/12373

PR: https://git.openjdk.org/jdk/pull/12373