Thanks. Just found out from this tutorial that using jitpack it's pretty simple, like 3 minutes and it's done!
I've been playing with bintray, and gradle scripts for a while, it needs a lot of customization to build all the correct files, keys but finally it uploaded to bintray with just one gradle task. Then we need to wait for jcenter to approve the package.
It's a lot of configuring for something that should be simpler.