RFR: 1698: Warning not to force push/rebase can be made clearer

[Zhao Song]

Rephrased the second sentence of the warning not to force push/rebase.

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Commit messages:
 - SKARA-1698

Changes: https://git.openjdk.org/skara/pull/1441/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1441&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1698
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1441.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1441/head:pull/1441

PR: https://git.openjdk.org/skara/pull/1441