[jdk13u-dev] RFR: 8283444: Bump update version for OpenJDK: jdk-13.0.12

[Yuri Nesterenko]

Regular switch to a new version on the start of a season.

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Commit messages:
 - Bump update version for OpenJDK: jdk-13.0.12

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/331/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=331&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283444
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/331.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/331/head:pull/331

PR: https://git.openjdk.java.net/jdk13u-dev/pull/331