RFR: 8274031: Typo in StringBuilder.readObject

[Joe Darcy]

Fix of a typo in the javadoc of StringBuilder,readObject, as previously reported to core-libs-dev:

https://mail.openjdk.java.net/pipermail/core-libs-dev/2021-September/081277.html

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Commit messages:
 - Fix for JDK-8274031.

Changes: https://git.openjdk.java.net/jdk/pull/5592/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5592&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274031
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5592.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5592/head:pull/5592

PR: https://git.openjdk.java.net/jdk/pull/5592