RFR: 1340: Correct email domain not always used when adding a contributor to a PR

[Zhao Song]

Now, the email domain for additional contributors is always the default "openjdk.org" domain because we hardcoded it.

To resolve this issue, we should use the domain in jcheck configuration file.

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Commit messages:
 - SKARA-1340

Changes: https://git.openjdk.org/skara/pull/1513/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1513&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1340
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1513.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1513/head:pull/1513

PR: https://git.openjdk.org/skara/pull/1513