Improvement to release script

Description

Based on https://github.com/OpenAPITools/openapi-generator/pull/647/commits/beaf2a56dc678cf0d8c5ffb468a6e7a128c9f84e, we can further automate the release process by replacing previous stable version (e.g. 3.1.1) with the latest stabe version (3.1.2)

openapi-generator version

Latest master

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/pull/647

Suggest a fix/enhancement

We will revise ./bin/utils/release_version_update.s accordingly.