RFR: JDK-8320940: Fix typo in java.lang.Double

[Joe Darcy]

Typo fix to to the new text added in JDK-8295391.

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Commit messages:
 - JDK-8320940: Fix typo in java.lang.Double

Changes: https://git.openjdk.org/jdk/pull/16872/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16872&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320940
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16872.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16872/head:pull/16872

PR: https://git.openjdk.org/jdk/pull/16872