RFR: 8278168: Add a few missing words to the specification of Files.mismatch

[Pavel Rappo]

Please review this trivial fix.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.java.net/jdk/pull/6679/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6679&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278168
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6679.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6679/head:pull/6679

PR: https://git.openjdk.java.net/jdk/pull/6679