### _Why are the changes needed?_
The upgrade section states <code>Kyuubi server supports **stop** gracefully</code>. Update to <code>Kyuubi server supports **stopping** gracefully</code>
### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible
- [ ] Add screenshots for manual tests if appropriate
- [ ] [Run test](https://kyuubi.readthedocs.io/en/master/develop_tools/testing.html#running-tests) locally before make a pull request
Closes#4864 from mans2singh/ISSUE-4863.
Closes#4864
5e853f84e [mans2singh] Updated key features section
Authored-by: mans2singh <mans2singh@yahoo.com>
Signed-off-by: Cheng Pan <chengpan@apache.org>
974fa73cac