RFR: JDK-8300867: Fix document issues in java.io

[Per Minborg]

This PR fixes a couple of typos in the documentation.

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Commit messages:
 - Update copyright year
 - Fix javadoc issues

Changes: https://git.openjdk.org/jdk/pull/12142/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12142&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300867
  Stats: 39 lines in 6 files changed: 0 ins; 0 del; 39 mod
  Patch: https://git.openjdk.org/jdk/pull/12142.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12142/head:pull/12142

PR: https://git.openjdk.org/jdk/pull/12142