RFR: SKARA-725: Rename git-pr-reviewer --add to git-pr-reviewer --credit

Mon Nov 2 17:27:42 UTC 2020

Hi!
The patch renames the add option to the credit in accordance with the change in the `/reviewer` command on OpenJDK Github bot.

I was unable to find any related documentation that should reflect  this change. If something needs to be updated, kindly point me to it and I'll do the needful changes.

Thanks.
Regards,
Kartik

-------------

Commit messages:
 - git-pr reviewer rename add option to credit

Changes: https://git.openjdk.java.net/skara/pull/938/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=938&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-725
  Stats: 7 lines in 1 file changed: 0 ins; 2 del; 5 mod
  Patch: https://git.openjdk.java.net/skara/pull/938.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/938/head:pull/938

PR: https://git.openjdk.java.net/skara/pull/938