RFR: JDK-8278130: Failure in jdk/javadoc/tool/CheckManPageOptions.java after JDK-8274639

[Hannes Wallnöfer]

Please review a simple fix in `CheckManPageOptions.java` that adds "--link-modularity-mismatch" to the group of javadoc options missing in the man page.

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Commit messages:
 - JDK-8278130: Failure in jdk/javadoc/tool/CheckManPageOptions.java after JDK-8274639

Changes: https://git.openjdk.java.net/jdk/pull/6664/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6664&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278130
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6664.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6664/head:pull/6664

PR: https://git.openjdk.java.net/jdk/pull/6664