Change maven storage Github to Maven Central

[gyuguen]

Currently, Github's repository is beta and is checking credentials when approached.
It's inconvenient because you need a certificate to use it simply.
Proceed to change to Maven Central.

• Reference
  https://maven.apache.org/repository/guide-central-repository-upload.html
  https://dzone.com/articles/publish-your-artifacts-to-maven-central
  https://www.albertgao.xyz/2018/01/18/how-to-publish-artifact-to-maven-central-via-gradle/