Migrate to Maven Central

[bearlysophisticated]

JFrog just announced that they'll be shutting down JCenter, keeping it as a read-only package repo:
https://jfrog.com/blog/into-the-sunset-bintray-jcenter-gocenter-and-chartcenter/

Key dates are:

• March 31st 2021: No more submissions will be accepted to Bintray, JCenter

Hence RxPermissions should also be migrated to another maven repository like Maven central.