RFR: JDK-8262269: javadoc test TestGeneratedClasses.java fails on Windows

[Jonathan Gibbons]

Fix test to work on Windows.

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Commit messages:
 - JDK-8262269: javadoc test TestGeneratedClasses.java fails on Windows

Changes: https://git.openjdk.java.net/jdk/pull/2702/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2702&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262269
  Stats: 4 lines in 2 files changed: 1 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2702.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2702/head:pull/2702

PR: https://git.openjdk.java.net/jdk/pull/2702