RFR: 8318059: Typo is javafx.scene.Mode.usesMirroring comment

[Prasanta Sadhukhan]

Corrected the typo

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Commit messages:
 - Typo fix

Changes: https://git.openjdk.org/jfx/pull/1260/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1260&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318059
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1260.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1260/head:pull/1260

PR: https://git.openjdk.org/jfx/pull/1260