This issue aims to improve the `merge-spark-pr` script.
- `[WIP]` is useful when we show that a PR is not ready for merge. Apache Spark allows merging `WIP` PRs. However, sometime, we accidentally forgot to clean up the title for the completed PRs. We had better warn once more during merging stage and get a confirmation from the committers.
- We have two kinds of PR title in terms of the ending period. This issue aims to remove the trailing `dot` since the shorter is the better in the PR title. Also, the PR titles without the trailing `dot` is dominant in the commit logs.